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Math Help - Simplify and verify.

  1. #1
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    Simplify and verify.

    Hey guys,

    the task: Simplify and verify.

    (-x^2 + x) (7x^2 + 3x -9)
    my calculation:
    = -7x^4-3x^3+9x^2+7x^3+3x^2-9x
    = -7x^4+4x^3+12x^2-9x

    Verification: x = 1

    -7x^4+4x^3+12x^2-9x
    = -7(1)^4+4(1)^3+12(1)^2-9(1)
    = -7+4+12-9
    = 0

    (-x^2 + x) (7x^2 + 3x -9)
    = (-1^2+1) (7(1)^2+3(1)-9)
    = (1+1) (7+3-9)
    = (2) (1)
    = 2

    Something is wrong in my verification calculations, because both solutions should agree. Could somebody please explain my mistake?
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  2. #2
    Forum Admin topsquark's Avatar
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    Re: Simplify and verify.

    Quote Originally Posted by ford2008 View Post
    (-x^2 + x) (7x^2 + 3x -9)
    = (-1^2+1) (7(1)^2+3(1)-9)
    = (1+1) (7+3-9)
    Lines 3. -1 + 1 = 0, not 2.

    -Dan
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