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Math Help - Method of Substitution

  1. #1
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    Method of Substitution

    y=x^3-x^2-1
    y=x^2+15x-1
    i completely forgot how to do this. i know method of elimination, but it says i gotta use substitution. any ideas?
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  2. #2
    MHF Contributor red_dog's Avatar
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    Substitute y from the first equation in the second equation:

    x^3-x^2-1=x^2+15x-1\Rightarrow x^3-2x^2-15x=0\Rightarrow x(x^2-2x-15)=0

    Then x=0 or x^2-2x-15=0

    Now solve the quadratic, then replace x and find y.
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