explain xkcd - User contributions [en]

816: Applied Math

2023-01-03T22:12:23Z

172.71.142.171: /* Explanation */

{{comic
| number = 816
| date = November 8, 2010
| title = Applied Math
| image = applied_math.png
| titletext = Dear Reader: Enclosed is a check for ninety-eight cents. Using your work, I have proven that this equals the amount you requested.
}}

==Explanation==
{{w|Donald Knuth}} is a {{w|computer scientist}} who has written several computer science textbooks and he offers {{w|Knuth reward check|monetary rewards}} for anyone finding errors in his publications. The first error found in each book is worth US$2.56 (256=28 is a very important number in the IT domain). Other suggestions are worth less than $2.56, but a check is still sent out if Dr. Knuth finds them to be reasonable.

[[Megan]] uses a proof to invalidate logic itself. (Of course, this means that her proof paradoxically renders itself meaningless. If logic has been disproven, her proof has no value.) According to the logic symbols [[File:contradiction.png]] at the bottom of the proof, she has proved that "the proposition (statement) is true and the proposition is false," i.e. "something is both true and false." (Specifically, ∴ means "therefore", ''P'' represents that a proposition is true, ∧ stands for "and", and an overbar negates a proposition (so ''P'' represents that a proposition is false) The negate symbol, ¬, is also used for this purpose when placed in front of a symbol). If someone were to prove this, it would indeed derail the very foundation of logic and result in the {{w|principle of explosion}}, which was referenced in [[704: Principle of Explosion|a previous comic]].

Since most of the content of computer science textbooks is fundamentally based on logic, Megan's proof obviously spells doom for Dr. Knuth's, as each instance of logic can now be considered an error. After Megan's friend confirms the validity of her proof, Megan writes a letter to Dr. Knuth to collect her money for the 1,317,408 errors in {{w|The Art of Computer Programming}} at $2.56 each. According to the amount Megan demands as a reward, she apparently considers this textbook to have an average of more than 400 instances of logic per page (if she has the latest edition of each volume).

The title text is the reply from Dr. Knuth, in which he uses Megan's logic-disproving proof against her by claiming — with no logical explanation — that the amount of money she is in fact due as a reward is only 98 cents. In logic, from a contradiction (such as "P∧P") can be inferred any statement, including that $3,372,564.48 = $0.98. He does this presumably to a) get out of paying her over three million dollars, b) demonstrate his contempt for or disbelief in her proof, and/or c) to show her, rather passive-aggressively, that she herself is not exempt from any ill effects resulting from her proof. If logic is proved to be false, then all mathematics are proved false and 3,372,564.48 = 0.98. Dr. Knuth could have also given her nothing, as 0 would equal 0.98 which would equal 3,372,564.48.

The title of the comic, "Applied Math," is a play on {{w|Applied mathematics}}, "mathematical methods that are typically used in science, engineering, business, and industry," as opposed to {{w|pure math}}, which focuses exclusively on abstract concepts. Instead of using math to calculate something like the speed of a falling object, Megan uses it for an ostensibly more frivolous reason: to gain a huge reward via a proof of dubious validity.

==Transcript==
:[Ponytail is standing at a whiteboard considering a logical proof. The proof assumes ''P'' and deduces ''P'' ∧ ''P''.]
:Ponytail: Wow. I can't find fault with your proof.

:[Ponytail is still looking at the white board, the frame expands to show Megan walking away, rubbing her hands together in an evil manner.]
:Ponytail: You've shown the inconsistency — and thus the invalidity — of basic logic itself.
:Megan: Excellent. On to step two...

:[Megan sits down at a desk and begins to write.]
:Dear Dr. Knuth,

:[She continues to write.]
:I am writing to collect from you the $3,372,564.48 I am owed for discovering 1,317,408 errors in ''The Art of Computer Programming...''

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Donald Knuth]]
[[Category:Logic]]

Talk:135: Substitute

2022-12-05T18:32:57Z

172.71.142.171:

[[User:Rikthoff|Rikthoff]] ([[User talk:Rikthoff|talk]]) The issue date is off, as i can't find a create date for the image. Can anyone fix?

:Yes, I've fixed the date on the page. [[User:Lcarsos|lcarsos]] ([[User talk:Lcarsos|talk]]) 15:30, 14 September 2012 (UTC)

1. It takes the raptor 25m/s / 4m/s^2 = 6.25s to reach it's top speed, during which I can run 6.25s * 6m/s = 37.5m. Add on my 40m head start, and I can reach a spot 77.5m away from the raptor before he gets me. In the same time, the raptor can run 4m/s^2 * (6.25s)^2 / 2 = 78.125m. I'm eaten before he's fully up to speed.
Therefore, I have to solve for when the raptors location, r(t) = 4m/s^2 * t^2 /2 - 40, and my location, m(t) = 6m/s*t, are equal. Dropping units, we get 2t^2 -40 = 6t, or 2t^2 - 6t - 40 = 0. Dividing by 2 I get t^2 - 3t - 20=0. Using the quadratic equation, I get (3 +/- sqrt(89))/2, roughly equal to 6.217s and -3.217s. Plugging that back into m(t), I get 37.302m for my terminal run. [[User:Blaisepascal|Blaisepascal]] ([[User talk:Blaisepascal|talk]]) 22:18, 14 September 2012 (UTC)

I don't think there is enough information to solve the second problem, because you don't know how fast the non-injured raptors go. Unless you take that information from the first problem. But then, how fast does the wounded raptor accelerate? You would have to find the angle where the wounded and the closest non-wounded raptor would meet you at the same time. [[Special:Contributions/213.127.132.140|213.127.132.140]] 17:17, 5 September 2013 (UTC)

With all three raptors and you running at top speeds, I don't think you get caught by the injured raptor and uninjured raptor at the same time. I believe that you must run directly towards the wounded raptor and the two non-injuried raptors will reach you simultaneously before you and the injured raptor meet, and you cannot do better. After all, you can try to run directly away from an uninjured raptor, but you will lose ground to it at a rate of 25-6=19 m/s (but, it is worst for the other uninjured raptor). By running directly at the injured raptor, you lose ground from it at the rate of 10+6=16 m/s. However, if you can accelerate at a rate far above the raptors, I think you could change directions so fast that one raptor could not catch you. However, I am not sure you can keep away from all three indefinitely. --DrMath 04:01, 24 October 2013 (UTC)

I did the math and if you run directly towards the wounded raptor it will catch you before the uninjured raptors do. (It would be better to run directly away from the uninjured raptor than it would be to run towards it, but that still not the answer.) As you would cover ~8m if you ran at the wounded raptor and survive for ~1.33s where as the uninjured raptors (assuming they rundirectly towards the point you meet the wounded raptor would take ~2.9s to reach this point. [[Special:Contributions/162.158.178.116|162.158.178.116]] 00:35, 8 October 2016 (UTC)

For 1 and 2 the solution depends on whether the raptors can accelerate at 2m/s, or they actually increase their speed at this rate. If they just accelerate, It should be possible to do tight circles, and even wind yourself slowly towards another location. I believe this is possible even treating yourself and the raptors as point masses. [[Special:Contributions/2.102.215.18|2.102.215.18]] 13:19, 17 July 2013 (UTC)

This could also be a parody of Snape substituting for Lupin (Harry Potter and the Prisoner of Azkaban) in the Defense against Dark Arts class. Snape assigns homework on werewolves, in the hopes of one of the students connecting the dots. Here, Randall might be trying to get the students to suspect that Mrs.Lenhart might be a raptor (out of sympathy, or just being a classhole?). Also [[155]]. [[Special:Contributions/208.124.118.63|208.124.118.63]] 18:58, 1 October 2013 (UTC)BK201

There is a problem with the test, as Mr. Munroe wrote it: Question #1 says that a raptor has a top speed of 25 m/s, but question #3 says "Remember, raptors run at 10 m/s...". Furthermore, question #2 says an injured raptor runs at 10 m/s.
:The way I resolved that was that raptors wouldn't be able to run straight long enough to reach their top speed inside of a building. [[Special:Contributions/108.162.237.161|108.162.237.161]] 23:53, 27 April 2015 (UTC)

BTW, the answer to question #2 is: run straight toward the injured raptor. The uninjured raptors will run toward you and the injured raptor. Just as you get close to the injured one, slide under his legs. Because he is injured, the uninjured raptors will feast on him instead of you. [[Special:Contributions/173.245.55.227|173.245.55.227]] 20:58, 13 December 2013 (UTC)

:This presumes the raptors are cannibalistic. -Pennpenn [[Special:Contributions/162.158.2.221|162.158.2.221]] 05:30, 15 June 2015 (UTC)

::In the original Jurassic park book, the little children get chased through the hatchery, and they try to use a baby raptor to distract the raptors chasing them, but the small raptor gets ripped to shreds. Raptors are merciless and horrible beings. Randall is right to hate them.[[User:RedHatGuy68|RedHatGuy68]] ([[User talk:RedHatGuy68|talk]]) 01:28, 29 October 2015 (UTC)

::I solved it by being a t-rex and just eating the raptors. It's amazing how many math problems become easier when you're a t-rex. [[Special:Contributions/162.158.255.69|162.158.255.69]] 23:29, 16 September 2015 (UTC)

:::So many problems become easier it seems by becoming a T-Rex.{{unsigned ip|172.69.34.30|23:53, 9 November 2022}}
::::But not that of tying your shoelaces. [[Special:Contributions/141.101.99.151|141.101.99.151]] 02:40, 10 November 2022 (UTC)

What if they're utahraptors or nanotyranus [[Special:Contributions/108.162.245.120|108.162.245.120]] 07:14, 13 October 2016 (UTC)

Question 3 is inaccurate: Using the knowledge gleaned from the movie, we can only assume raptors can open some doors. i.e., those with lever handles. Given their anatomy, it is unlikely that they would achieve proficiency with the more standard round-knob-based doors. --Electro-- [[Special:Contributions/108.162.221.130|108.162.221.130]] 07:13, 9 September 2017 (UTC)

Life finds a way.

Should this be in 'comics featuring Miss Lenhart'? The comic does not show her, although it does mention her.

135: Substitute

2022-12-05T18:29:05Z

172.71.142.171: /* Explanation */

{{comic
| number = 135
| date = July 31, 2006
| title = Substitute
| image = substitute.png
| titletext = YOU THINK THIS IS FUNNY?
}}

==Explanation==
This comic refers to the film ''{{w|Jurassic Park (film)|Jurassic Park}}'', a 1993 movie based on the 1990 novel by {{w|Michael Crichton}}. The film centers around a billionaire who bought an island and opened a zoo or theme park for dinosaurs that he has cloned from DNA recovered from blood found in fossilized mosquitoes. After a computer programmer shuts down the security systems to steal embryos for a rival company, several of the creatures, among which are the {{w|Velociraptor}}s subject of this comic, run loose and try to devour every human in the theme park.

Velociraptors (often shortened to "raptors") are a species of relatively small, carnivorous {{w|dinosaur}} that play a central role in the original film, as well as its sequels. In the film, packs of Velociraptors antagonize the main characters at various points, even entering buildings. According to newer researches, the Velociraptors in the film were erroneously based on the {{w|Utahraptor}} species of dinosaur. Unlike the movie, in which they are depicted as having a reptilian skin, both species of dinosaur in reality are theorized to have been feathered. The word "raptor" also refers to modern {{w|Bird of prey|birds of prey}}.

[[Randall]] is asked to substitute for [[Miss Lenhart]] in math class. The first page of the test he devises contains three questions, which have the recurring theme of humans running from said velociraptors. For the answers, see the [[135: Substitute #Trivia|trivia section.]] As Randall says in the comic: "This material is more vital than anything you've ever learned," the joke being that Randall is somehow fearful that such a thing could happen.

Velociraptors, and in particular, the irrational fear of being attacked by them in the modern world, [[:Category:Velociraptors|appear several times]] in [[xkcd]]. This is the second such instance; the first is [[87: Velociraptors]]

In the title text, Randall asks the kids whether they find this possibility humorous (and they rightfully should, considering that the chances of such a thing occurring are astronomically low{{Citation needed}}).

==Transcript==
:[In a classroom, the board says "Math" on the top-left corner, and "Mr. Munroe" in the middle. A Cueball portrays Randall, standing in front of it, speaking to the class.]
:Randall: Miss Lenhart couldn't be here today, so she asked me to substitute.
:Randall: I've put out your tests. Please get started.

:[A student in the first row raises the exam paper and says:]
:Student: Mr. Munroe, Miss Lenhart never taught us this.

:Randall: That's because Miss Lenhart doesn't understand how important certain kinds of math are.
:Student: But this just looks--
:Randall: This material is more vital than anything you've ever learned
:Student: But--
:Randall: No buts.

:Randall: This is a matter of life and death.

:[Excerpt from the exam paper.]
:<tt>Name: _________</tt>

:[A stick figure is standing, hands over head. A velociraptor is running towards it.]

:<tt>1. The velociraptor spots you 40 meters away and attacks, accelerating at 4 m/s^2 to its top speed of 25 m/s. When it spots you, you begin to flee, quickly reaching your top speed of 6 m/s. How far can you get before you're caught and devoured?</tt>

:<tt>2. You're at the center of a 20m equilateral triangle with a raptor at each corner. The top raptor has a wounded leg and is limited to a top speed of 10 m/s.</tt>

:[A stick figure is shown in the above situation. The picture has a legend "<tt>(Not to scale).</tt>"]

:<tt>The raptors will run toward you. At what angle should you run to maximize the time you stay alive?</tt>

:<tt>3. Raptors can open doors, but they are slowed by them. Using the floor plan on the next page, plot a route through the building, assuming raptors take 5 minutes to open the first door and halve the time for each subsequent door. Remember, raptors run at 10 m/s and they do not know fear.</tt>

==Trivia==
*Answers to the first two questions can be found in [https://web.archive.org/web/20150326152959/http://fora.xkcd.com/viewtopic.php?f=7&t=120&start=40 this topic] on the forum board.
**The first is 37.30194339616981 meters.
**The second is 57.19 degrees to either side of the wounded raptor, if the raptors at each instant move towards the current position of the person.
**The second is 59.83 degrees to either side of the wounded raptor, if the raptors' trajectories are optimal for catching the person as quickly as possible.

{{comic discussion}}
[[Category:Comics featuring Miss Lenhart]]
[[Category:Comics featuring Randall Munroe]]
[[Category:Comics with color]]
[[Category:Velociraptors]]
[[Category:Jurassic Park]]
[[Category:Math]]
[[Category:Physics]]
[[Category:Comics featuring Cueball]]

2705: Spacetime Soccer

2022-12-03T22:58:40Z

172.71.142.171: Undo revision 300332 by 172.70.82.166 (talk) austrian freemasonry

{{comic
| number = 2705
| date = November 30, 2022
| title = Spacetime Soccer
| image = spacetime_soccer_2x.png
| imagesize = 1x1px
| noexpand = true
| titletext = [[File:Murdered Rwandan Tutsi, January 1964.png]]
}}

==Explanation==
TOTAL ŊIGGЁR DEATH

Megan

2022-12-03T22:57:44Z

172.71.142.171:

{{Infobox character
| image = Megan.png‎
| imagesize = 150px
| caption = Megan
| first_appearance = [[16: Monty Python -- Enough]]
}}It actually exists, a cure for cancer.

It's a machine that generates an elecrtrical frequency that you pick for a certain kind of cancer. This frequency kills only the cancerous cells, but may harm any neighboring cells. But that's about it. You just put it on your body and after a set amount of hours, you're either fine or you have to wear it for longer. The machine itself was created in the 1910s, but it never caught steam because no one in the medical community wanted to use it. Why cure cancer when you can treat it and wring people out of every cent they've got?

It makes me really fucking angry because if you know what Chemotherapy is, you know that if you have to take it, you've already lost. Chemo is just a powerful fucking poison being run through your body that kills cells, and when you take it i, the hope is that it kills your cancerous cells, but it will also harm literlally everyhting else it comes into contact with. I've had several friends who had to watch their family members slowly fucking die because their doctors treated them by running bleach and rat poison through their veins.

I know it's real and it works because it's the only reason my grandfather and aunt, both of which whom I love, are still with me.

I don't have a source for this shit. Believe me, or don't, I don't care.
'''Megan''' is a [[stick figure]] character in [[xkcd]]. She is the second-most frequently appearing character, after [[Cueball]], and the most frequently appearing female character. She does not necessarily always represent the same character from comic to comic. She is essentially the female equivalent of Cueball, representing the every-woman to his {{w|everyman}}. This is less clear than for Cueball as there are several comics, where there are [[:Category:Multiple Cueballs|multiple Cueball-like figures]], any of whom could be called Cueball.

There are very few comics where this happens with Megan-like characters, with the few including [[139: I Have Owned Two Electric Skateboards]], [[173: Movie Seating]], [[1409: Query]], [[1496: Art Project]], [[430: Every Damn Morning]], [[2040: Sibling-in-Law]], and in [[1951: Super Bowl Watch Party]].

Of course she also appears several times in some of the comics with [[:Category:Large drawings|large drawings]], like [[1110: Click and Drag]]. Often this should be seen as different small comics, where there is just one Megan in each story. In [[1608: Hoverboard]], however, there are two identical Megans at the bottom rear end of the Destroyer, where one is talking to the other. As opposed to with Cueball, an example where this is a serious problem for Megan has yet to be found.

Megan does sometimes appear to have slightly specific personality traits; she has quite odd habits, and is sometimes shown to be very focused and intent on a goal. However, as explained above this is not a general rule for a given Megan character.

==Name==
''Explain xkcd'' originally referred to this character as "Cutie" (complementing "Cueball" with a matching first syllable). But then a "Cutie" was given a specific name, Megan, in [[159: Boombox]] and later in for instance [[215: Letting Go]], [[420: Jealousy]], [[478: The Staple Madness]], and [[654: Nachos]]. The name was also used without displaying a drawing of Megan in [[596: Latitude]] and in the title text of [[627: Tech Support Cheat Sheet]].

The name Cutie was then changed to Megan. If this rule should be followed generally, then Cueball should be re-named Rob after [[276: Fixed Width]] (and the [[:Category:Comics featuring Rob|other 8 times]] a Cueball has been named Rob in total). But as mentioned above this was not to be.

She can also be drawn under a different name as in [[672: Suggestions]], where a sexy image of her, hair hanging loose over her face, is called Susie. And in [[1221: Nomenclature]] Megan is called Mrs. Whatsit in the transcript provided in the comic source. In [[734: Outbreak]] Cueball and Megan are named Ryan and Laura, but that is a movie, so they could be actors called Cueball and Megan in real life...

A character that looked a lot like Megan, but with somewhat longer hair and a much meaner attitude, was distinguished from her as [[Black Hat]]'s girlfriend [[Danish]]. A similar long-haired version of Megan also appeared in [[1730: Starshade]], although without the attitude.

==History==
Early comics often feature Megan-style characters who may or may not be identified as Megan. [[Randall]] appears not to have standardized his character lineup early in the comic's run, and as a result, certain early female characters sometimes have similar hair to Megan, but some different features.

The name (or even pseudonym) "Megan" may be reference to a lost love of Randall's, given that he wrote a passive-aggressive toast for Megan's wedding in [[420: Jealousy]] about how he was madly still in love with her, put across in a way that would generally ruin the day for everyone involved. We also see this earlier in [[215: Letting Go]].

Several of the [[:Category:Cancer|comics about cancer]] have Megan representing Randall's fiancée (later wife).

==Characteristics==
Megan is distinguished by her black shoulder-length hair which generally appears to be parted in the middle in front, and is draped behind what are presumably her (undrawn) ears. It is shorter than the character of similar appearance, [[Danish]]. Megan also tends to behave less deviantly than Danish does.

Megan's age is sometimes given, like in [[1409: Query]], we learn that she is 30 or younger, implying that she was born in 1984, but in [[630: Time Travel]], we learn she was born in 1983 and in [[2178: Expiration Date High Score]], we can calculate that she was born in 1982 or earlier. Since Randall just uses Megan for any woman not too old or young, and since the figure is not explicitly named "Megan" in any of these comics, these are three different characters and we cannot put an age on Megan.

== Trivia ==
*Actually the first comics to be released using Megan not number 16, [[16: Monty Python -- Enough]] but [[24: Godel, Escher, Kurt Halsey]] because of the release order on [[LiveJournal]], see details in the trivia for both [[16: Monty Python -- Enough#Trivia|Monty Python -- Enough]] and [[24:_Godel,_Escher,_Kurt_Halsey#Trivia|Godel, Escher, Kurt Halsey]].

==See also==
*[[:Category:Comics featuring Megan|Comics featuring Megan]].
*[[Danish]].
*It was at some point suggested that Megan and Cutie should be un-merged? In relation to a similar suggestion that Cueball and Rob should be merged. But nothing came of the [http://www.explainxkcd.com/wiki/index.php/explain_xkcd:Community_portal/Proposals#Merge_Cueball_.26_Rob discussion.]

{{navbox-characters}}

[[Category:Characters]]

1615: Red Car

2022-12-03T03:01:48Z

172.71.142.171: /* Explanation */

{{comic
| number = 1615
| date = December 11, 2015
| title = Red Car
| image = red_car.png
| titletext = That guy only drives an alkaline car to overcompensate for his highly acidic penis.
}}

==Explanation==
This comic is a take on the common stereotype that men who drive large, expensive, and/or ostentatious cars (such as sports cars, highly modified cars, and lifted pick-up trucks), do so in order to compensate for insecurity about their manhood. Typically this is summarized as saying they are compensating for having small penises.

{{w|Cyan}} is a greenish-blue color that is not a basic color term in most languages. It is the {{w|complementary color}} to red in the CMYK (subtractive) or RGB (additive) color models.

[[Megan]], upon seeing [[Hairy]] drive past in a red convertible, tells [[Cueball]] that Hairy must be compensating for his cyan colored penis.

This comic thus generalizes the original stereotype to an assumption that men drive cars that compensate for problems/properties with their penis (e.g. large car for small penis). Under this principle, a red car would complement (be the opposite of) a cyan penis. This is of course ridiculous, as red cars are quite common and cyan penises either extremely rare or nonexistent{{Citation needed}}; but maybe Megan doesn't realize this, or is joking.

There may also be a reference to the Doppler shift, where an object moving away (such as a galaxy) appears slightly redder than its true color. On the contrary, objects moving closer shift blue or cyan. However, cars cannot go nearly as fast to create a change in the perceived color.

In the title text another pair of opposites are mentioned: {{w|acid}} and {{w|alkaline}}. Acidity is an extremely odd property to try to compensate for with one's choice of car. Additionally, most penises share the same basic chemical composition and therefore the same acidity. If your penis can be described as "highly acidic", you probably have a major medical problem. Again this could be Megan's lack of understanding, and since some models of cars are called [http://jalopnik.com/5327974/why-cant-you-get-a-nice-basic-car-these-days basic cars] (instead of a special red convertible) she could make the (wrong) assumption that they drive a basic car to compensating for their acidic penises.

Thus, this comic is referring to the actual definition of "compensation", which means to balance something out by adding another. If an image has too much red value on the RGB scale, one could shift it more towards neutral by adding to the blue value. And a solution with a low (acidic) pH can be neutralized by mixing it with an alkaline solution to bring its pH to a neutral value. (Whereas a big car will not balance out a small penis!{{Citation needed}})

An alternative interpretation to this just being about opposites is that of a more specific big vs small compensation. In each case the car represents something larger than Hairy's penis: in the comic - red has a "bigger" (longer) wavelength than cyan. Similarly in the title text, alkali has a "bigger" (higher) ph than acid. Of course against this alternative is that red has a smaller energy/frequency than cyan and that you would often talk about stronger acids, making a low ph count as strong, not small! Finally the joke loses some value if it is still just a matter of big/small rather than actual properties of the penis that are being compensated for.

==Transcript==
:[Megan and Cueball are standing next to an intersection as Hairy drives by in a red convertible.]
:Megan: I bet he just drives that car to overcompensate for his cyan penis.

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Hairy]]
[[Category:Penis]]