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    cubic polynomial

    the cubic polynomial x^3 +ax^2 + bx - 8 where a and b are constants has factors x+1 and x+2. find values a and b



    i'm thinking you expand (x+2)(x+1) to get the quotient of x^2 + 3x + 2 but i'm not sure


    would be so grateful for some help thanks
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    Quote Originally Posted by gracey View Post
    the cubic polynomial x^3 +ax^2 + bx - 8 where a and b are constants has factors x+1 and x+2. find values a and b



    i'm thinking you expand (x+2)(x+1) to get the quotient of x^2 + 3x + 2 but i'm not sure


    would be so grateful for some help thanks
    Let the third factor be (x + c).

    Then
    (x + 1)(x + 2)(x + c) = (x^2 + 3x + 2)(x + c) = x^3 + (c + 3)x^2 + (3c + 2)x + 2c

    Match up the coefficients.

    -Dan
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