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Proof with real numbers

  1. Oct 10, 2009 #1
    1. The problem statement, all variables and given/known data

    x and y are real numbers. prove that if x2-4x=y2-4y and x not equal to y, then x+y=4.

    2. Relevant equations

    n/a

    3. The attempt at a solution

    I tried using cases and making x and y positive and negative or even and odd, and that didnt work. then i tried completing the square on both sides and I got x=y.
    please help~
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 10, 2009 #2

    Dick

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    Science Advisor
    Homework Helper

    Move all the terms to one side. x^2-y^2=(x+y)(x-y). Factor out an (x-y).
     
  4. Oct 10, 2009 #3

    Mark44

    Staff: Mentor

    Dick, I think you mean "move all the squared terms to one side."
     
  5. Oct 10, 2009 #4

    Dick

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    Science Advisor
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    I meant what I said. I was counting on the OP finish it from there.
     
  6. Oct 10, 2009 #5

    Mark44

    Staff: Mentor

    OK, fair enough.
     
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