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Homework Help: Simultaneous equations

  1. Oct 13, 2011 #1
    1. The problem statement, all variables and given/known data

    Sure I could do this by looking at the mark scheme, but i need to know HOW and WHY, so that in the future i can do these equations by myself. Thanks :)

    by elimenating y, solve the simeltaneous equation

    2. Relevant equations

    x^2 + y^2 = 10
    y = 2x - 5

    3. The attempt at a solution

    I thought i might have to make 5 the subject for the equation for this to work?

    Outside of this my solution was to square it but that didn't work either..
  2. jcsd
  3. Oct 13, 2011 #2


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    Staff Emeritus
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    If y = 2x - 5 , what is y2 ?
  4. Oct 13, 2011 #3
    (2x - 5) 2 ?
  5. Oct 13, 2011 #4


    Staff: Mentor

    Now replace y2 in the first equation with this expression, and solve the resulting quadratic.
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