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Math Help - 2=1 ?

  1. #1
    Newbie
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    2=1 ?

    Hello,

    I have a question regarding a problem that my prof gave me:

    x=y
    then
    x = xy
    x- y= xy- y
    (x-y) (x+y) = (x-y) y
    x+y= y
    y+y=y
    2y=y
    which would mean that 2=1

    Can someone explain me where the problem is?
    Thanks in adavance!
    Last edited by mr fantastic; January 27th 2010 at 04:13 AM. Reason: Edited post title
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  2. #2
    MHF Contributor
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    Quote Originally Posted by chrisjohnston View Post
    (x-y) (x+y) = (x-y) y
    x+y= y
    Hi

    This is a well known problem
    You cannot divide by (x-y) since it is equal to 0
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  3. #3
    Senior Member
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    Mathematical fallacy - Wikipedia, the free encyclopedia

    Scroll to Division by zero for your question.



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  4. #4
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    Thanks for your quick replies guys!!!!
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