Explain xkcd: It's 'cause you're dumb.
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The circumference of a circle is
C = 2πr, where ''r'' is the radius of the circle. Randall then makes a footnote about ''r'', but he uses <sup>2</sup>. This creates a typographical ambiguity, since the superscript 2 can also be an exponent (as in ''x''<sup>2</sup>). Randall's formula now looks like a strange hybrid of the correct formula and A = πr<sup>2</sup>, which is the formula for the ''area'' of the circle. |+|
The circumferenceof a circleis 2πr, where ''r'' is the radiusof the circle. Randall then makes a footnote about ''r'', but he uses <sup>2</sup>. This creates a typographical ambiguity, since the superscript 2 can also be an exponent (as in ''x''<sup>2</sup>). Randall's formula now looks like a strange hybrid of the correct formula and the formula for the ''area'' of the circle.
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|−|In the title text , r' normally means the derivative of r, and r'<nowiki/>' the double derivative of r, whereas ' can be read as "prime" , while '<nowiki/>' can refer to inches. |+|
the title text'the derivativeand the derivativeof r, read as "prime"can refer to
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Revision as of 15:34, 11 March 2013
The circumference C of a circle is 2πr, where r is the radius of the circle. Randall then makes a footnote about r, but he uses 2. This creates a typographical ambiguity, since the superscript 2 can also be an exponent (as in x2). Randall's formula now looks like a strange hybrid of the correct formula and the formula for the area of the circle: A = πr2.
As for the title text; r′ and r″ is Lagrange's notation for the derivative and the second derivative of r, respectively. Since ′ is the prime symbol, r′ is often read out as "r-prime". "Prime" can mean first or original, and "Earth Prime" is a term sometimes used in works of fiction involving parallel universes (e.g. the DC Multiverse), to refer to our Earth, or to a world with a minimum of divergence points from Earth as we know it. (The radius of Earth Prime would thus not differ much from the radius of the Earth; 6 371 km.)
The double prime (″) also designates inches.
- Circumference of a circle:
- 2The circle's radius
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- Tau x Radius, superscript 2
- Since tau is more commonly used for the Golden Ratio, that's a silly idea. 188.8.131.52 11:13, 23 September 2013 (UTC)
- You may be confusing tau with phi. I've never seen the golden ratio represented by anything other than phi. I've also never seen tau representing anything other than 2pi. 184.108.40.206 19:25, 10 May 2014 (UTC)
- Leaves one wondering what the superscript 1 refers. -- 220.127.116.11 (talk) (please sign your comments with ~~~~)
- It's 2πr2, not τr2. —18.104.22.168 05:37, 11 March 2013 (UTC)
- You're missing the point. τ == 2π and is considered better than using π by some people -- 22.214.171.124 (talk) (please sign your comments with ~~~~)
- Only for very loose definitions of "better." 126.96.36.199 14:59, 11 March 2013 (UTC)
- Whoa! Never heard about that before, but after 2 hrs or so, I think I'm getting convinced! Check this site out: http://tauday.com/ What do you think? –St.nerol (talk) 18:06, 11 March 2013 (UTC)
- Ok so τ might make more sense than π but as comic 1179 pointed out, both pi-day and tau-day are wrong. Tharkon (talk) 13:23, 3 August 2014 (UTC)
- I think tau is pointless. Using tau what then happens to Euler's famous formula, the most beautiful equation of them all? Pi shows up in so many different ways and places in mathematics. Tau appears pretty much only in the formula for a circle's circumference. Why bother needlessly proliferating symbols? J Milstein (talk) 18:17, 11 March 2013 (UTC)
- Surface area of a sphere is 2τr^2, or if you want to get pi in there πd^2 188.8.131.52 (talk) (please sign your comments with ~~~~)
- RE: Euler's Identity: e^(tau*i) - 1 = 0 --Max Nanasy (talk) 18:27, 11 March 2013 (UTC)
- Ok, that works J Milstein (talk) 17:05, 13 March 2013 (UTC)
- Why not just e^(tau*i) = 1. Do you routinely do 2 + 2 - 4 = 0?184.108.40.206 20:31, 13 March 2013 (UTC)
- --Max Nanasy (talk) 00:35, 14 March 2013 (UTC)
- I think Euler only did that because he disliked negative numbers. It really is less a deal than people make of it.220.127.116.11 03:02, 15 March 2013 (UTC)
- Also, it uses the five most important constants in mathematics: e, π (or τ), i, 1, and 0. Curtmack (talk) 20:33, 30 April 2013 (UTC)
- The tau variant of Euler's identity above, e^(tau*i)=1, appears to miss the point. Normally, a positivt number to the power of any real number is positive. Thus i could be any normal number. Well, not any number. i could be 0 and the equation will hold. With pi however, e^(pi*i)=-1, i must be magical. /David A 18.104.22.168 23:53, 9 November 2013 (UTC)
- The tau manifesto fairly well convinced me that all occurances of π in mathematics utimately trace back from the formula C = 2πr. If so, π naturally enter calculations as 2π. Can anyone find a counterexample to this thesis? –St.nerol (talk) 00:29, 14 March 2013 (UTC)
- How could there be a counter-example? I think it is true. In complex analysis, it really should be 2π, and thus Gaussian integrals. And then number theory applications. Even this neat result really stems from trig identities, so it really is a result for 2π. 22.214.171.124 02:59, 15 March 2013 (UTC)
- From what I understand, the thesis from the tau-proponents is that 2*pi is the fundamental natural constant, and that virtually every time that pi shows up without the factor 2, there originally was a factor two that was cancelled out. –St.nerol (talk) 01:53, 12 March 2013 (UTC)
- For everyone who suddenly started a debate about 2pi and tau: http://xkcd.com/1292/ 126.96.36.199 06:58, 4 May 2014 (UTC)
Not completely sure Earth Prime is from Sliders, but it's true it's the only one named exactly that ... -- Hkmaly (talk) 09:54, 11 March 2013 (UTC)
There's also a Prime Earth now. Just so DC can screw with us. Hogtree Octovish (talk) 10:40, 11 March 2013 (UTC)
I still don't get it.188.8.131.52 12:41, 11 March 2013 (UTC)
- If you don't get it, you don't need to get it J Milstein (talk) 18:07, 11 March 2013 (UTC)
Well, that was lame. --184.108.40.206 17:19, 11 March 2013 (UTC)
This comic illustrates the strategy of "The Unconsummated Asterisk", from the essay "Mathmanship" by Nicholas Vanserg (available at ).
The other side of the asterisk gambit is to use a superscript as a key to a real footnote. The knowledge‐seeker reads that S is – 36.714 calories and thinks "Gee what a whale of a lot of calories" until he reads to the bottom of the page, finds footnote 14 and says "oh."
For bonus points, Randall could have used also "Pi-Throwing":
For example every schoolboy knows what π stands for so you can hold him at bay by heaving some entirely different kind of π into the equation. The poor fellow will automatically multiply by 3.1416, then begin wondering how a π got into the act anyhow, and finally discover that all the while π was osmotic pressure. If you are careful not to warn him, this one is good for a delay of about an hour and a half.
) 19:01, 11 March 2013 (UTC)
- Another good one is π as a symbol for profit in financial discussions. -DrGaellon (talk | contribs) 23:23, 25 March 2013 (UTC)
I believe the current description of prime as denoting derivatives is true but irrelevant. Since the area and circumference refers to geometry (not really calculus), it's more likely that the title text is referring to the common use of primes in geometry. For example, there might be two or more parallel lines that are denoted by x, x′, x′′, etc. Wikipedia also notes another geometric use of prime: "if a point is represented by the Cartesian coordinates (x, y), then that point rotated, translated or reflected might be represented as (x′, y′)." S (talk) 23:32, 11 March 2013 (UTC)
that is so wrong, i feel my mind corrupted now. -- Anarcat (talk) 23:57, 11 March 2013 (UTC)
This explanation was hillarious -- where is the up-vote button ?? Spongebog (talk)
- +1 Smperron (talk) 16:33, 13 March 2013 (UTC)
So, where's todays comic? How many times has Randal been late?220.127.116.11 16:15, 13 March 2013 (UTC)
- Today's comic was posted just a few minutes ago. I'm anxiously awaiting its explanation as it picks on a programming language I'm not familiar with (possibly SQL). Smperron (talk) 16:33, 13 March 2013 (UTC)
It uses pseudocode. The new one is about sorting algorithms in general, not any particular language. 18.104.22.168 17:00, 13 March 2013 (UTC)
Perhaps it's just me, but did no one see the "square the circle" gag...? --22.214.171.124 09:24, 14 March 2013 (UTC) No one but you saw the square-the-circle gag, because it's not there. For it to be there, it would require this: (2πr)² J Milstein (talk) 15:31, 14 March 2013 (UTC)
This one threw me for a loop for the longest time because I learned to use πd to find circumference, not 2πr. Anyone else learn that way? (Knowing how my brain works, it is equally possible I taught myself to use πd as a shortcut, and was in fact taught 2πr by my teachers.) Boct1584 (talk) 22:20, 31 March 2015 (UTC)
I thought the joke in the title text was that primes can refer to successive derivatives. 126.96.36.199
05:05, 19 August 2015 (UTC)