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Foiled Again
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Foiled Again

by courtney.gibbons on July 29, 2009 at 8:29 am
Chapter: comics
└ Tags: algebra, students, teaching
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Discussion (16) ¬

  1. Noah
    July 29, 2009, 10:15 am | #

    When I was in pre-calculus, there was a 10-Day Pre-Cal syllabus. One of the days was, “Show them the video of the student factoring x^2 + y^2 = (x+y)^2 and getting HIT BY A TRAIN” so that made me laugh a lot!

  2. Jim Vaught
    July 29, 2009, 10:29 am | #

    Alas! Would that the world were a commutative ring of characteristic 2…

  3. Harald Schilly
    July 29, 2009, 10:50 am | #

    But my computer says:

    sage: R. = GF(2)[]
    sage: (x+y)^2
    x^2 + y^2

    ;)

  4. Sylvia S.
    July 29, 2009, 2:25 pm | #

    Okay, this comic goes on my office door. (Of course, that is why Z_2 is so nice.)

  5. Sylvia S.
    July 29, 2009, 2:26 pm | #

    Oh, I just saw Jim Vaught’s comment. He already got the commutative ring of characteristic 2. Foiled again.

  6. foofoo
    July 29, 2009, 7:28 pm | #

    mod 2 and it works fine

  7. John
    July 29, 2009, 9:34 pm | #

    We call this the freshman dream.

  8. Invisibules
    July 30, 2009, 3:08 am | #

    I only came here to suggest trying it in Z_2, but since you beat me to it, I could point out that it also works in Z_1 …

  9. 31459265
    July 30, 2009, 3:52 am | #

    Another one: anticommutative rings!

  10. Ethan
    July 30, 2009, 5:36 am | #

    It works for boolean algebra too, though admittedly I’ve never seen exponents used to represent iterated AND gates. That would be a seriously cute notational convention.

  11. Patrick
    July 30, 2009, 11:07 am | #

    I’m a math tutor at a college campus…I’m definitely going to hang this up in the room. Printed out very large.

  12. Kevin
    August 6, 2009, 2:47 pm | #

    Doesn’t every equation work in Z_1?

  13. Nancy
    August 27, 2009, 3:26 pm | #

    well
    this is funny….but also stupid mistake

  14. Maxtwo
    June 11, 2010, 9:09 pm | #

    It works in any Z_p. (x+y)^p == x^p+y^p (p)

  15. Per Persson
    October 10, 2011, 10:22 am | #

    (x + y)^2 = x^2 + y^2 is valid if xy + yx = 0.

  16. Carlos
    December 23, 2017, 8:36 am | #

    Sorry if this is a silly question, but shouldn’t it be foils powers, rather than foils products? Of course a power just indicates products, but the distributive rule works for products by one term.

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