Difference between revisions of "2070: Trig Identities"

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
(Explanation)
(Fixed typo)
Line 17: Line 17:
 
The third and fourth line is made by treating the trigonometric function as a product of variables rather than a function and then using the above identities to create words. e.g. sin = b/c -> cin = b/s (this could also be a reference to the C++ cin).
 
The third and fourth line is made by treating the trigonometric function as a product of variables rather than a function and then using the above identities to create words. e.g. sin = b/c -> cin = b/s (this could also be a reference to the C++ cin).
  
The third line is composed of puns: e.g., cin=b/c describes how the C++ cin function sucks, cas=0/c is read "California's South is Orange County".
+
The third line is composed of puns: e.g., cin=b/s describes how the C++ cin function sucks, cas=0/c is read "California's South is Orange County".
  
 
The second to last line performs some algebra on the individual letters of <math>(\mathrm{tan}\ \theta)^2=\frac{b^2}{a^2}</math> as a setup to the last line.  The last line takes the formula <math>distance=\frac{1}{2}at^2</math> "from physics" and plugs it into the equation of the previous line, doing some algebra to replace <math>at^2</math> with <math>distance2</math> and expanding <math>(na)^2</math> into <math>nana</math> to get the final equation, <math>distance2banana=\frac{b^3}{\theta^2}</math> .  This is valid algebra only if the trigonometric operators are taken as variable products rather than operators, but this is a common misconception encountered when people first learn trigonometry.  The distance equation is the distance a constantly accelerating object initially at rest moves in a given length of time t, most often used to find how far an object dropped from rest will fall under the influence of gravity in a given amount of time (or how long it will take to fall a given distance).
 
The second to last line performs some algebra on the individual letters of <math>(\mathrm{tan}\ \theta)^2=\frac{b^2}{a^2}</math> as a setup to the last line.  The last line takes the formula <math>distance=\frac{1}{2}at^2</math> "from physics" and plugs it into the equation of the previous line, doing some algebra to replace <math>at^2</math> with <math>distance2</math> and expanding <math>(na)^2</math> into <math>nana</math> to get the final equation, <math>distance2banana=\frac{b^3}{\theta^2}</math> .  This is valid algebra only if the trigonometric operators are taken as variable products rather than operators, but this is a common misconception encountered when people first learn trigonometry.  The distance equation is the distance a constantly accelerating object initially at rest moves in a given length of time t, most often used to find how far an object dropped from rest will fall under the influence of gravity in a given amount of time (or how long it will take to fall a given distance).

Revision as of 01:40, 10 November 2018

Trig Identities
ARCTANGENT THETA = ENCHANT AT TARGET
Title text: ARCTANGENT THETA = ENCHANT AT TARGET

Explanation

Ambox notice.png This explanation may be incomplete or incorrect: Please only mention here why this explanation isn't complete. Do NOT delete this tag too soon.
If you can address this issue, please edit the page! Thanks.

This comic shows several real and fictitious trigonometric identities. Most of the identities past the second line are "derived" by applying algebraic methods to the letters in the trig functions, which violates the rules of math, since the trig functions are operators and not variables.

The first line are well known trigonometric functions. The second line contains the lesser known reciprocals of the trigonometric functions in the first line.

The following identities are made up and are increasing in absurdity. The comic reflects on the confusion one gets when working more intensely with these identities, since there are a lot of hidden dependencies between them.

The third and fourth line is made by treating the trigonometric function as a product of variables rather than a function and then using the above identities to create words. e.g. sin = b/c -> cin = b/s (this could also be a reference to the C++ cin).

The third line is composed of puns: e.g., cin=b/s describes how the C++ cin function sucks, cas=0/c is read "California's South is Orange County".

The second to last line performs some algebra on the individual letters of (\mathrm{tan}\ \theta)^2=\frac{b^2}{a^2} as a setup to the last line. The last line takes the formula distance=\frac{1}{2}at^2 "from physics" and plugs it into the equation of the previous line, doing some algebra to replace at^2 with distance2 and expanding (na)^2 into nana to get the final equation, distance2banana=\frac{b^3}{\theta^2} . This is valid algebra only if the trigonometric operators are taken as variable products rather than operators, but this is a common misconception encountered when people first learn trigonometry. The distance equation is the distance a constantly accelerating object initially at rest moves in a given length of time t, most often used to find how far an object dropped from rest will fall under the influence of gravity in a given amount of time (or how long it will take to fall a given distance).

There seem to be (at least) two errors in the formulars:

  • \mathrm{cas}\ \theta=\frac{o}{c} seems to be derived from \cos\theta=\frac{a}{c} but to reach "cas" from "cos" one has to divide by "o" and multiply by "a". This would lead to \frac{a^2}{co} on the right hand side.
  • In the identity \sin\theta\sec\theta=\mathrm{insect}\theta^2 one of the "s"'s has turned into a "t". This can be found by combining \cos\theta=\frac{a}{c}, \mathrm{cas}\ \theta=\frac{o}{c}, which show o=a, and s=\frac{1}{c^2\theta}. Using this with \csc\theta=\frac{c}{b} you can "prove" c=b and then with with \cot\theta=\frac{a}{b} you can find t=\frac{1}{c^2\theta}=s. The casual reader is more likely to see a 'poetic stretch' from the sound of saying 'sin sec' together.

The title-text is an anagram. Due to the commutative property of multiplication (which states that order does not affect the product), these equations are equivalent if treated as individual variables as earlier. Another layer of absurdity is added in that the variable Theta is spelled out and broken into its letters, which are then treated as individual variables. (The arctangent referred to here is the inverse tangent, a one-sided inverse to the tangent function. You would not normally write \arctan\theta, since the theta in the comic refers to an angle, and the arctangent has an angle as its value rather than as its argument; however, using theta here is merely unconventional, not forbidden.) The arctangent generally produces theta, the meaning of it being taken on theta being poorly understood. Randall here elucidates, via tongue-in-cheek algebraic proof, that taking a second arctangent of theta produces magical effects.

Transcript

Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.
[Inside a single frame comic a right-angled triangle is shown. The shorter sides are labeled "a" and "b" and the hypotenuse has a "c". All angles are marked: the right angle by a square and the two others by arcs. One arc (enclosed by "a" and "c") is labeled by the Greek symbol theta (θ).]
[Supposed trigonometric functions of the marked angle θ are shown:]
sin θ = b/c
cos θ = a/c
tan θ = b/a
cot θ = a/b
sec θ = c/a
csc θ = c/b
cin θ = b/s
cas θ = o/c
tab θ = b²/n​a
bot θ = a/c → boat θ = a²/c → stoat θ = a²/c · s​t/b
tan θ ( = b/a = b/a · c/c = b/c · c/a = sin θ sec θ ) = insect θ²
(tan θ)² = b²/a² ( → t²n²a⁴ = b²/θ² → a​t²b​a(n​a)² = b³/θ²
from physics: distance = 1/2 a​t² → ) distance2banana = b³/θ²
[Caption below the frame:]
Key trigonometric identities


comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!

Discussion

I am confused by the insect line. This seems to be true only if s=t. 141.101.96.209 19:03, 9 November 2018 (UTC)

I added a note regarding how similar it sounds to 'sinsec'. 172.68.51.154 01:47, 10 November 2018 (UTC)
That one and the `cas` aren't making any sense to me. GreatBigDot (talk) 20:02, 9 November 2018 (UTC)
Oh, the casinus is much important to... What was it? --Dgbrt (talk) 20:15, 9 November 2018 (UTC)
cas is realtively easy... it is cos(theta)=a/c -> cs(theta)=ao/c -> cas(theta)=o/c; when you realise that the top one isn't zero but o it clicks 141.101.96.209 23:35, 9 November 2018 (UTC)
You made the same error Randall did: you divided by 'o' on the left and multiplied on the right. I think the theme of the page is expanding significantly upon common math errors that were already humorous, like the common proof of 5=3 by dividing and multiplying by zero. The error here is in line with the theme of casual beginner errors. 172.68.51.154
You can see cin is derived from sin by swapping the positions of c and s. Likewise, Switching the a and o in cos(theta) = a/c gives cas(theta) = o/c i.e. no need for multiplicative consistency. The rule of treating things as a product of terms is implemented fully in the following lines. 162.158.91.83 11:23, 12 November 2018 (UTC)
 sin \theta = b/c leading to cin \theta = b/s is algebraically valid if you interpret sin as the product of s, i, n by multiplying both sides by c/s. It is not valid to just "swap" two letters in one equation that is part of a system of equations. You could do the same trick and get cas \theta = a^2/oc from cos \theta = a/c or start with sec \theta = c/a and get cas \theta = c/e. Note for all equations except cas \theta = o/c and switching an s to a t to find tan \theta = insect \theta^2, the equations can be correctly derived by treating trig functions as product of single letter variables and algebraically manipulating them. Jimbob (talk) 16:59, 12 November 2018 (UTC)
I think insect is.. a bug.. ;) Smerriman (talk) 20:18, 9 November 2018 (UTC)

Is Enchant at target a magic:the gathering reference? AncientSwordRage (talk) 20:55, 9 November 2018 (UTC)

I think it is a Magic: The Gathering reference. Although it is phrased oddly. You'd think it would be "at target enchantment", rather than "target at enchantment". --Dryhamm (talk) 21:04, 9 November 2018 (UTC)
Likely, it refers to the bigbox retailer, Target. 172.68.58.233 (talk) (please sign your comments with ~~~~)
To me it sounds more like a reference to a nerdy video game, where a certain object worked like this, turning e.g. BEAM OF DARK ENERGY into a BAKED FERRY GNOME 108.162.246.11 21:53, 12 November 2018 (UTC)
Voila - s=t. -- Elliott (talk) (please sign your comments with ~~~~)
That was incredible! (assuming previous poster discovered the extrapolated proof in the description) 172.68.51.154 01:47, 10 November 2018 (UTC)
Combining \cos\theta=\frac{a}{c} and \mathrm{cas}\ \theta=\frac{o}{c} allows you to conclude a^2 = o^2, not a=o. 162.158.146.10 (talk) (please sign your comments with ~~~~)

Somebody added a comment on puns, e.g. that "cin sucks". More explanation is needed. It looks like some kind of a meta-joke. If you ask why, and start interpreting, you see that "b/c" == "because". It might be the answer to why the puns line should be removed, though. 172.68.51.154

For the Bot->Boat->Stoat line, this comes from the word game where you add/change letters to make a new word. Start with bot=a/c, multiply by a on both sides gets boat=a^2/c. Multiply by st on both sides and divide b on both sides gets Stoat=a^2/c*St/b. 162.158.78.166 (talk) (please sign your comments with ~~~~)

Uh... people... THE NAME GAME? Hello? https://en.wikipedia.org/wiki/The_Name_Game 162.158.79.107 (talk) (please sign your comments with ~~~~)

Checking through the math, just working from the real trig identities, without considering Randall's at-first-glance questionable identities like cas theta = o/c, basically everything that does not have a factor of d or 2 in it is equal to 1, and d is equal to 1/2, which then establishes the more questionable identities as tautological, 1=1. 162.158.142.100 04:09, 10 November 2018 (UTC)


\sec\theta = sect \eta 141.101.104.71 13:36, 10 November 2018 (UTC) AndreasH

Am I the only one who saw t²n²a⁴ as "tuna"? 172.68.58.233 14:17, 10 November 2018 (UTC)

Yes. 162.158.75.190 (talk) (please sign your comments with ~~~~)

\frac{d}{dx}\sec x=\sec x\tan x= sex tanks. Probably not Douglas Hofstadter (talk) 21:36, 11 November 2018 (UTC)

I thought "distance 2 banana" had to be a reference to QBasic's Gorillas game. "Enchant at target" could refer to the banana exploding when it hits something. mrpsbrk 162.158.123.91 (talk) (please sign your comments with ~~~~)