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Math Help - Cubic Equation

  1. #1
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    Cubic Equation

    I know cubic equations must have the form  Ax^3 + Bx^2 + Cx + D = 0, and I know how to solve that type of equation by doing long division etc:


    However I got this cubic question,


    x^3-3x^2+4


    It doesn't have the same form as above and it's put me right off knowing what to do. I tried to simplify it ( x(x^2+3x) +4) but I got no where fast. So any starters of where I should start to factorize would be very helpful!
    Last edited by Kaynight; October 22nd 2008 at 10:34 PM.
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  2. #2
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    Quote Originally Posted by Kaynight View Post
    I know cubic equations must have the form  Ax^3 + Bx^2 + Cx + D = 0, and I know how to solve that type of equation by doing long division etc:


    However I got this cubic question,


    x^3-3x^2+4


    It doesn't have the same form as above and it's put me right off knowing what to do. I tried to simplify it ( x(x^2+3x) +4) but I got no where fast. So any starters of where I should start to factorize would be very helpful!
    It has the same form as above, with C=0.
    You can notice that -1 is a solution, hence x+1 divides your polynomial. It remains to compute Q(x) such that x^3-3x^2+4=(x+1)Q(x).
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  3. #3
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    Quote Originally Posted by Laurent View Post
    It has the same form as above, with C=0.
    You can notice that -1 is a solution, hence x+1 divides your polynomial. It remains to compute Q(x) such that x^3-3x^2+4=(x+1)Q(x).
    Many Thanks!
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