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Math Help - 1=2!

  1. #1
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    1=2!

    This is a very well know puzzle, but for those who don't know it...

    X=Y
    X-Y=0
    2X-2Y=0
    2X-2Y=X-Y
    so..
    2(X-Y)=1(X-Y)
    2=1 !!

    This proves that 2=1. Which is impossible. Who can show where these equations are wrong?
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  2. #2
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    e^(i*pi)'s Avatar
    Joined
    Feb 2009
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    West Midlands, England
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    Quote Originally Posted by Corum View Post
    This is a very well know puzzle, but for those who don't know it...

    X=Y
    X-Y=0
    2X-2Y=0
    2X-2Y=X-Y
    so..
    2(X-Y)=1(X-Y)
    2=1 !!

    This proves that 2=1. Which is impossible. Who can show where these equations are wrong?
    Dividing by 0 is undefined as pretty much everyone on the forums knows
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  3. #3
    Newbie
    Joined
    Jan 2010
    Posts
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    I should have labeled it pre-playschool puzzle.
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  4. #4
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    Joined
    Dec 2009
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    Kyoto
    Posts
    16

    FYI

    see also:
    http://www.mathhelpforum.com/math-he...oof-1-2-a.html

    for more 'proofs' that show 1=2.
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