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Thread: functions

  1. #1

    Thread Starter
    Addicted Member dolor's Avatar
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    functions

    Express q as a function of p, given that one root of x^2 + px + q = 0 is twice the other.
    - you've been privileged to read a post by Miz

  2. #2
    pathfinder NotLKH's Avatar
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    x2 = 2*x1

    (x-x1)(x-2*x1) = x^2+p*x+q
    x^2-(2*x1+x1)*x+2*(x1^2) = x^2+p*x+q
    x^2-(3*x1)*x+2*(x1^2) = x^2+p*x+q

    So:
    p = -3*x1
    q = 2*(x1^2)

    or:

    x1 = (-1/3)p
    so:

    q = (2/9)*(p^2)

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