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Homework Help: How to solve equation?

  1. Jun 24, 2008 #1
    please help me in solving this question.
    3x^2+xy-y^2=81 ; x+y=7

    I will be thankful to you
  2. jcsd
  3. Jun 24, 2008 #2

    D H

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    We don't do your homework here. Show some work, please.
  4. Jun 24, 2008 #3
    Also it's not a question:
    "3x^2+xy-y^2=81 ; x+y=7 ??"
  5. Jun 24, 2008 #4


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    Hi Aladin! :smile:

    Hint: do the easy equation first.

    So x = … ? :smile:
  6. Jun 24, 2008 #5


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    Gold Member

    Find y in terms of x and substitute...
  7. Jun 24, 2008 #6
    this isnt even precalculus its basic algebra
  8. Jun 24, 2008 #7
    it is not my home work I am just trying to solve it because I am learning basic math.so please help me in solving this equation
  9. Jun 24, 2008 #8
    Just follow everyone's advice and solve find x in terms of y or vice versa y in terms of x and substitute back into your equation.
  10. Jun 25, 2008 #9
    after you solve in terms of the other with one equation you have to plug in for the other equation
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