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Math Help - factoring a quadrinomial

  1. #1
    Junior Member
    Joined
    Oct 2008
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    factoring a quadrinomial

    Hi,

    I'm trying to factor -x^3+3x+2 so I can find the zeros (well its actually part of a linear algebra prob. for which I need to find the eigenvalues) but I can't figure out how to factor it... even after consulting tutorial sites to dust off my factoring skills :S...

    Help?
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  2. #2
    Member
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    -x^3+3x+2=-x^3+x+2x+2=-x(x^2-1)+2(x+1)=-x(x-1)(x+1)+2(x+1)=
    (x+1)[-x(x-1)+2]=(x+1)(-x^2+x+2)

    -x^2+x+2=0
    D=1+8=9
    x1=-1
    x2=2
    -x^2+x+2=-(x+1)(x-2)

    (x+1)(-x^2+x+2)=-(x+1)(x+1)(x-2)=-(x+1)^2(x-2)
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