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An Accidental Ode to MSWord Hotkeys

This was triggered by the discussion on news.ycombinator.com/item?id=5305055.

I feel that much of the perceived difference between modefulness and modelessness is in your head (doesn't make it less real, I admit). Look, are you familiar with the concept of a hotkey sequence? They're the most visible in Emacs, where many commands are bound to a sequence such as C-x C-s.

Everything we do on a keyboard is part of a sequence. In Vim, you can type :wqa to execute a command, and if someone made a similar binding in Emacs, it would be represented in their notation as S-; w q a, and more importantly, it would feel different to many people. Because in Vim, : makes you enter a state where you can type anything you want in a free-input field, and in this case you type wqa. In Emacs, pressing S-; will make the minibuffer display S-; while nothing happens, indicating that you've begun a hotkey sequence. As you press each key, they'll show up: S-; w q a … It feels like you're in the same state throughout, where Emacs is doing nothing and waiting for you to reach a sequence that is bound to a command. In particular, you feel constrained. In the Vim equivalent, you can backspace whereas in Emacs if you press the wrong key you have to re-do the sequence.

But you're ultimately doing the same thing with your fingers. Someone recording your fingers wouldn't know if you were executing an Emacs command, a Vim command, or merely typing ":wqa" into the body of a blog post.

When you type the word "hi", you are executing the sequence of pressing the h key followed by the i key. I grant this is a silly example, but I need to show that every keystroke comes in sequences. Sequences are the universe, the backdrop of everything that happens during keyboard input.

Modern editors typically have hotkey sequences consisting of a single step. Obviously, a single hotkey is always better than two in a sequence. By the same token, two hotkeys are better than three, and so on. You want the fewest number of steps in the sequence, for convenience. Cheers to modern editors!

This is complicated by the question of which hotkeys you put in the sequence. If they are single letters like w q a, fine! If they are C-c C-x p, not so good. The latter looks like three keystrokes but is four, or five if you count having to release the Ctrl key before pressing p, which I find at least as annoying as having to press it in the first place.

Now, back to modern editors: they typically have hotkey sequences consisting of a single step. But what hotkeys? Almost always a combination like Ctrl-F, which is two keystrokes minimum.

Given that they're modeless, of course they have to do it this way. And it's not so bad. The thing about Vim Normal mode is that single-hotkey commands don't even need modifiers, you can just press f, no Ctrl.

The drawback is that you have to enter a "mode", which sounds weird.

To get around this, I will describe another basic concept of keyboard input, which has many names but that I'll call a hydra. A hydra is a many-headed beast of Greek myth, that grew new heads whenever one was cut off. It's also a way of making hotkey sequences more persistent. For example, suppose that you wanted to execute the following commands:

C-c C-x p
C-c C-x l
C-c C-x a

Lot of work, right? But, if the sequence C-c C-x is a hydra, then what you have to type is

C-c C-x p l a

That is, the first parts of the sequence don't have to be retyped.

The way hydras are typically implemented in Emacs is that they're nonpersistent (compared to a Vim mode, see later). As soon as you hit some key (let's say r) that isn't bound to anything in the hydra, it exits the hydra and does what that key would have done instead, i.e. instead of it trying to execute the equivalent of C-c C-x r you simply type the letter r onscreen. The hydra is exited trivially, unlike modes in Vim that have to be exited with the ESC key.

Now the meat of the topic. All that a mode is, is a type of hydra. The Vim Normal mode is a hydra that starts with ESC, and it's very broad, having many different keybinds coming after ESC. We might say that the hydra has one head for every key on your keyboard: there are none undefined. It's a persistent one, as it's not easy to exit. The escape hatch is the i key, which instead puts you in the Insert mode hydra (and doesn't insert the letter "i": it's a whole keystroke merely to change mode and do nothing more).

If you like to view it this way, all editors are constantly in a hydra, just one that doesn't need to be entered with any key beforehand. Modeless editors aren't modeless, they have one mode.

Now think about this: What is easier to press, Ctrl-F or Ctrl then F? Is it easier to press the D key and the F key at the same time, or to press them in sequence?

YMMV, but many feel that pressing two keys in sequence is more comfortable than two keys at the same time.

So over of pressing d and f together, we always prefer the sequence d and then f. What if the reason you do this is that 'd' puts you in a different mode, where the 'f' key will do what you want? Does it make a difference? In the Vim paradigm, yes: you will also have to exit that mode when you're done. Then it can be preferable to just press a chord such as Ctrl+F and not think about entering and exiting modes.

Suppose the mode wasn't persistent? I.e. suppose by pressing d you enter the mode, then by pressing f, you execute that command and return to the mode you were in previously.

Well. Then it's not a mode as most would define it, just a hotkey sequence. (It can be a hydra though: hydras may have both persistent and non-persistent heads, a mixture of those that grow back and those that don't)

If you want to take the classification to the extreme, each hotkey in a hotkey sequence is a small mode, a non-persistent one, wherein the next hotkey will do something it wouldn't have done otherwise. Emacs has hundreds or thousands of these small modes while Vim has three big modes. Most editors have one (by virtue of rejecting hotkey sequences altogether).

Microsoft Word is actually an exception. If you're a whiz with hotkeys there, you know what I mean: they use hotkey sequences (all of which start with Alt), though never with modifiers. It's like the best of Vim and Emacs: the modes are non-persistent and automatically exit (unlike Vim), and they don't need you to hold down the Ctrl key either (unlike Emacs). The only way to improve on this would be make some of those sequences into hydras, and correct me if I'm wrong, but I think Word has done that too.

Word is bad in so many ways, but it seems the keyboard input was competently designed.

Anyway, I hope modes don't feel weird now.

Keyboard design

What links here

  • 2023-09-13
Created (8 years ago)

Memorize memories of flashcards with flashcards

Combination of SRS and memory castles.

The basic memory castle

For the thought experiment, instead of flashcards, suppose you have a stack of cheatsheets. You wanna memorize them. You go and put the cheatsheets in a memory castle.

In mindspace, you can alter the cheatsheets – the words are no longer confined to A4 sheets, and art can be three-dimensional and include the sense of touch.

Obama's insight about blue suits can be represented by Obama wearing a blue suit, e.g. (Though the presence of a person would be overpowering, so persons should only be used for important insights. A framed Obama?)

For advanced potential, perhaps add smell to different rooms – if you focus inwardly on really feeling that smell, you kind of will smell it, regardless of what your flesh nose is sensing. And then, turn your attention to the room, and it should come back more easily. To mint new memory objects, it may help to go in meatspace to smell the appropriate thing for that room.

For example… an Indian-styled room, smelling of chai tea. Go smell some meatspace chai before even trying to envision it (because memory retcons itself, you may cause details to disappear forever).

Instead of words, you can have objects. Suppose you've read a book and written notes from it. Eventually these notes become a box of objects in your memory castle.

Merging with a Spaced Repetition System

Now make a small change to the thought experiment. Instead of representing what were originally paper cheatsheets, your memory objects represent what were originally flashcards. These flashcards still exist in your SRS, so they are now effectively duplicated.

Now start adding a new class of flashcard to the same SRS deck.

For this new class, you can put pictures of your memory rooms. Eventually you can even draw the objects you've created and put those drawings in SRS – so your SRS contains both the original flashcard and another flashcard that refers to the first one! (Option: attach a random image to every flashcard, well before turning them into memory objects. That way you can reuse those images)

Take care, don't create too many objects. You don't need as many flashcards as you think.

Memory objects can themselves hold memory objects. For example, in one room, you might find a bicycle (a Ribbing bike). On its saddle, you might find a Buddha statue. On his lap, you might find a flower. On the petals, you might find a fly. On the fly, you might find a crown. On the surface of the crown (really zoomed in), you might find a golden castle on a flat field of gold. Inside the castle, you might find a banquet. In the banquet, you will NOT find another Ribbing bike – don't reuse objects.

For a grace period, you practice on flashcards both on actual paper/SRS, and in the mindworld. Eventually, you may detach from the software and have it all in your head.

For true spaced repetition, try a Leitner system (inside the mindworld!). Arrange your objects. Hold them, smell them – every time you handle an object. Arrange them in a system. Not necessarily numeric. Just "on that desk" is recent stuff, "upstairs on that bookshelf" is old flashcards, "in the wine cellar behind that scary vampire nest and in front of the liliputian" is some old but important stuff. Re-use things from your life. The amphitheatre, some notes on love and relationships in Momo's room, with whom you can have a conversation while you're at it. You would of course draw your imagination of Momo's room often.

Sketch, sketch, sketch. No need to sketch the memory objects in use (you can if you want), just sketch the rooms, the 'bases'.

Use emotion. Fear (the scary vampire nest) is one. A narrow bridge…

Flashcard front: Buddha Flashcard back: Buddha with rose on his lap

Flashcard front: Rose Flashcard back: Rose with a fly

etc.

What links here

Created (9 years ago)

Calculus

Power rule

We learn this this high school: a function xn has the derivative nxn-1.

Proof example

Let's take the square root function x1/2. The power rule says this should result in 1/2 * x-1/2.

We'll prove it using the limit "as delta x goes to zero". Some people like to call that variable h or d, but we'll go with delta x.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

We cannot set delta x to zero, because it's sitting in the denominator. Let's change the expression. Using the difference of squares (a + b)(a - b) = a2 - b2, we multiply numerator and denominator by (a + b).

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Normally, when we cancel something from the denominator, we add a clause that it must be nonzero. Irrelevant/implicit when you're working with limits.

We're left with the expression node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 , and can now pretend that delta x is zero without breaking the equation. That's just node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 , or node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 , which fits the power rule.

Chain rule

A function f(x) that composes two functions g(x) and h(x) such that one is inside the other like: g(h(x)), will have the following derivative: g'(h(x)) * h'(x).

Note that in the first factor you neglect modifying the inner function.

Example: the derivative of sin(2x) is 2cos(2x), because you are deriving two functions: sin(something), and 2x. The derivative of 2x is just 2.

Aside: As you know, the sine of x derives to the cosine of x, but there are two functions in sine of x: the sine, and the x itself. What gives? Indeed you should derive both. But x derives to 1, which you just don't need to write.

Product rule

A product of two functions f(x) g(x) has the derivative f'(x) g(x) + f(x) g'(x).

For a product of three functions, derive "one at a time", leaving the rest untouched, for each term.

Function inputs

Take f(x).

  • Reflect across the x-axis: -f(x). This should be intuitive.
  • Reflect across the y-axis: f(-x)
  • Reflect across both axes: -f(-x)

Example: Periodic functions

sin(2x) är dubbelt så “snabb” som sin(x). sin(x/2) hälften så snabb. 2sin(x) gör kurvan dubbelt så hög, men ändrar inte svängningens frekvens. Dvs den når fortfarande 0 efter 1pi tid (alltså vid x=1pi). sin(x) + 2 förflyttar kurvan 2 steg uppåt, så att dess “noll-axel” är en horisontell linje som skär y vid 2.

TODO Plot a third-degree polynomial and paste images for the difference between f(x), -f(x), f(-x).

Odd and even functions

An even function is where f(-x) = f(x), i.e. symmetric, reflected across y-axis. An odd function is where -f(-x) = f(x). i.e. that if you reflect it across both axes, you end up with the same graph.

If there is a constant — an y-intersect offset from origin — it will fail to be odd.

A function is neither even nor odd when f(x) doesn't tell you anything about f(-x), i.e. when it isn't perfectly reflected across axes.

The terminology came from exponents of some functions, but the exponents don't necessarily determine it.

When the highest-degree exponent is odd, the function may be odd. When the highest-degree exponent is even, the function may be even.

What's a function

All these are functions:

  • sin x
  • x2
  • 2x
  • x
  • ln x
  • ex
  • 2x

A function evaluates to only one value for a given x.

Elementary function

Euclid's similarity cases

△ABC ≅ △DEF means triangle ABC is congruent to (has the same measurements as) triangle DEF.

Compare two triangles:

  1. Two pairs of sides being proportional and the angle between them the same => similar triangles.
  2. Any pairs of sides being proportional => similar. (??)
  3. Any pair of angles the same => similar. (??)

Partial fraction expansion

A way to change a rational expression into multiple terms, which is then easier for some purposes – like taking the derivative or integral, or doing a Laplace transform.

Part of elementary school in some countries…

Take an example. node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

First check to see what degree these polynomials are in. If the denominator has a lower degree, then you do a polynomial division, and then do the partial fraction expansion, okay? The technique is for stuff that you can't divide, like the remainder left by a polynomial division.

Now observe the denominator. What x makes it reach zero? That's 2. So you can factor out (x - 2), right? (Scribble a polynomial division of node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 with node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 )

We get an altered denominator: node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

You could also try to factor the second-degree expression we just got, but doing it in our head tells us it will not be possible in the reals. Skip it.

Now the aim of the technique is to set variables A and B, sometimes C etcetera:

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

A is a constant because the denominator is first-degree. You perceive the rule: the numerator should be one degree less.

To put the right-hand side over the same denominator, expand the fractions. You know how…

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Now you can just remove the denominator from both sides. Unfactor the RHS.

Logarithms

Addition: lg 5 + lg 5 = lg 25 Subtraction: lg 10 - lg 5 = lg 10/5 = lg 2

Exponents: lg 23 = 3 lg 2

Change of base formula

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Limits

"What is the limit of node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 when n goes to infinity?"

Solution: we want to do a variable substitution on the function inputs. We'll have to change the n out front so that it is something something 1/n. The expression above is equal to node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 .

Thereafter, subbing 1/n for x, we ask the limit of x as it goes to zero – because 1/infty goes to zero. We get the expression node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

What happens here? The solution lies in Standard limits. The limit goes to 1 * 1 = 1.

Standard limits🔗

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 x → 0   x → ∞ x → + ∞  
  node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1   node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1    
           
  node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1        
  node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1        
  node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1        

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Differential equation

Differential equations involve a function and its derivative, sort of. In a "first-order" differential equation, the highest order of derivative is one. In an "ordinary" differential equation, the function is of one variable.

If there is a requirement that the solution take on a particular value at a particular input, the exercise is called a `begynnelsevärdesproblem'.

You can plot the solutions to differential equations, in the form of a grid of 'directions' in a coordinate system: the tangent that a solution function would have at a given (x,y). `Riktningsfält'.

Now, by a linear differential equation, this is meant:

Take a generic equation node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 , and name the LHS node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 . Linearity will imply that node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 and that node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 . This is similar to linearity in other fields of math, no?

Solving a first-order differential equation

The simplest form of a first-order equation is node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 , which I will name A. A more general form is node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 To solve that one, turn it into A.

Choose a primitive node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 to the coefficient node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 for y. Multiply both sides of the equation with the so-called integrerande faktorn node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 . (Because node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 is nonzero for all x, the resulting equation is strictly equivalent!)

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Notice, that the LHS is the derivative of node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 ! That is neat since we are working on differential equations. Rewrite the equation as

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Now you can treat this as you would treat A. Namely, turn node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 into node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 (see my seminar writeups for another example):

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Applying this to the equation we got, we get

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Now you can divide both sides by node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 and get an expression for y. Insert whatever required values you were given for y and x to find out C, etc.

Fundamental Theorem of Calculus

Proves the useful formula of Insattningsformeln (PB 298), which is just the basic rule of how to integrate a defined interval.

Can also be used for (PB 298)

Optimization

Finding the "best" solution to a problem, like the maximum payoff or minimal material use. Involves finding asymptotes, zeros of derivatives, etc.

Continuity

A function is continuous around a point if it isn't undefined nor jumps to some unexpected value at exactly that point. Mathematically, the limit from both sides of that point is equal to the value of the function at that point.

Differentiability

Standard derivatives

The derivatives of common functions are as follows

f(x) f'(x)
sin x cos x
cos x -sin x
tan x node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1
cot x node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1
arcsin x node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1
arccos x node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1
arctan x node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1
arccot x node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Standard integrals

Implicit differentiation

When you work with unknown functions and use their derivatives, it's called implicit differentiation. Nothing to be scared of.

Absolute value

Taking the absolute value of a complex number lets you get rid of the "i".

Absolute equation

Consider the graph of an absolute value linear function like |x - 1|. It has two distinct segments, and no other notation would give it that shape. It's not a smooth function, it's two functions, depending on which x you're at.

So to rewrite |x - 1| without bar notation, make cases for different x. The quick way is to see where it becomes zero, which is at x=1. For the case of x>1, you can just remove the bars. For the case of x<1, also flip the signs.


It's easier with complex numbers. Consider the case of having a complex number inside bar notation, like |a + bi|. Rewriting it as a vector gives us a circle around origin, any point on which may be touched by the vector, but it's irrelevant - we want only the radius r in re{}.

Now consider the case of some unknown complex number z, plus other stuff: |z + 1 + i|. The origin of the "vector" z will now be at -1, -i, so this circle is centred off-origin.

Example solving the above: Set z := x + yi. Say its absolute value is 2. Write the equation.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

The last form can be recognized as Pythagoras.

After squaring, the equation resembles that of a circle:

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

[2024-04-22 Mon] Created Maclaurin/Taylor series

Standardutvecklingar

In these cases, θ is a number between 0 and 1 that depends on x and n.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 \hfill where node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 \hfill where node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Proofs for the above (PB )

Mean value theorem

Partial integration

What links here

  • Math
Created (9 years ago)

Trigonometry

Reciprocal identities

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1
node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Secant and cosecant not taught in Sweden.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

If you prefer expressing them in sine and cosine:

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Interestingly, note that tan is 1/cotan, but sine is not 1/cosine.

Offset identities

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Imagine the unit circle. Instead of starting at zero, you start at pi/2. Then, due to subtraction, you walk clockwise, not counterclockwise.

Unit circle

Inverse trig functions

There are different definitions of the domain of inverse trig functions. Multi-valued arcsin is a thing. Mathematica in particular might define the cotangent differently from Sweden. But here are the rules for basic-uni Swedish math.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

TODO Explain how to think, don't just make a reference table

Law of sines

We can use it to find stuff about nonright triangles.

Angle A, opposing side a;

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Num and denom can be swapped.

Law of cosines

Can tell you stuff about nonright triangles. Like with the Law of Sines, the capital letters denote angle opposing a side denoted in lower case.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

The Pythagorean Theorem is a special case of this Law.

Pythagorean identity

In Swedish, it's called trigonometriska ettan. cos2x + sin2x = 12

Should be obvious if you look at the unit circle and remember the Pythagorean Theorem.

Half-angle formula

Double-angle formula

sin(2x) = 2 sin(x) cos(x)

Proof?

Example: Find the sine of π/12

Using the double angle formula, we know that

sin(π/6) = 2 sin(π/12) cos(π/12).

We also know from our standard angles that sin(π/6) is 1/2. So

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

The reason I left cosine by itself is that we'll exploit the Pythagorean identity. First, let's square this thing.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Now, look at a different equation, the Pythagorean identity:

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

We have an expression for node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 , so replace it.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Multiply the equation so we're rid of the fraction.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Now, we can do variable substitution. Say node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 .

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Solve like any second-degree equation.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

So, given that we made y the squared sine of π/12, we square root the equation and get our answer.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

To figure out whether the plus or minus applies, test them. The result node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 is definitely larger than sin(π/12) ought to be, so the plus-minus sign should be a minus.

Euler's formula🔗

General form: e = cos(θ) + isin(θ)

Insert π and check the value. It gives you zero sin, -1 cos. So: e = -1. You quickly realize that inputting any multiple of pi will give you a real number.

Trig angle-addition formulas can be derived: substitute (a + b) for θ. Convert to cis(a + b) form. Perform the complex multiplication. The terms with i will correspond to the angle addition formula for sin, since the sine axis in the unit circle and the imaginary axis are both vertical. The terms without i then, of course, correspond to the angle addition formula for cos.

De Moivre's formula follows from Euler's formula. (cosθ + isinθ)n is (e)n, which by simple exponent rules is eiθn, which by definition is cos(nθ) + isin(nθ).

De Moivre's formula🔗

(cosθ + isinθ)n is equal to cos(nθ) + isin(nθ). You can state the cisθ in terms of Euler's formula to prove it.

Angle addition

To get the formula for tan, merely do the angle addition for sin, divided by angle addition for cos. Tan is sin/cos.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

Multiply both numerator and denominator by node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1 and you will get a simplified form.

node:internal/modules/cjs/loader:1228 throw err; ^ Error: Cannot find module 'katex' Require stack: - /home/kept/private-dotfiles/.config/emacs/texToMathML.js at Module._resolveFilename (node:internal/modules/cjs/loader:1225:15) at Module._load (node:internal/modules/cjs/loader:1051:27) at Module.require (node:internal/modules/cjs/loader:1311:19) at require (node:internal/modules/helpers:179:18) at Object. (/home/kept/private-dotfiles/.config/emacs/texToMathML.js:1:15) at Module._compile (node:internal/modules/cjs/loader:1469:14) at Module._extensions..js (node:internal/modules/cjs/loader:1548:10) at Module.load (node:internal/modules/cjs/loader:1288:32) at Module._load (node:internal/modules/cjs/loader:1104:12) at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:173:12) { code: 'MODULE_NOT_FOUND', requireStack: [ '/home/kept/private-dotfiles/.config/emacs/texToMathML.js' ] } Node.js v20.18.1

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