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Math Help - roots of cubic equations

  1. #1
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    roots of cubic equations

    the roots of the cubic equation
    x^3 - 15x^2 + px - 105 = 0

    are 5-k, 5 and 5+k
    Find the values of the constants p and k

    i dont know what to do or how to start please some one help!!
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  2. #2
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    Re: roots of cubic equations

    Quote Originally Posted by mathkid12 View Post
    the roots of the cubic equation
    x^3 - 15x^2 + px - 105 = 0

    are 5-k, 5 and 5+k
    Find the values of the constants p and k

    i dont know what to do or how to start please some one help!!
    perform synthetic division with a 0 remainder
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  3. #3
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    Re: roots of cubic equations

    sorry to say this but what!!!!!! synthetic devision >??
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  4. #4
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    Re: roots of cubic equations

    might want to look it up ... be sure to spell it right
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  5. #5
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    Re: roots of cubic equations

    Quote Originally Posted by mathkid12 View Post
    the roots of the cubic equation
    x^3 - 15x^2 + px - 105 = 0

    are 5-k, 5 and 5+k
    Find the values of the constants p and k

    i dont know what to do or how to start please some one help!!
    5 is a root so sub 5 into the equation and you will get p.
    In a cubic equation starting with x^3 the product of the roots is the constant term, in this case -105 So 5(5-k)(5+k)= -105
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