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Math Help - cubic function factoring

  1. #1
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    cubic function factoring

    Hi. I have to factor a cubic function expression for homework and it just has me stomped.

    x^3 - x^2 -5x -3

    currently i have x+1 and x-3 as a factor (I did long division and got 0R for both of them but i cant figure out the third factor.

    Appreciate any help
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ffezz View Post
    Hi. I have to factor a cubic function expression for homework and it just has me stomped.

    x^3 - x^2 -5x -3

    currently i have x+1 and x-3 as a factor (I did long division and got 0R for both of them but i cant figure out the third factor.

    Appreciate any help
    what? i don't see how you got yourself in this predicament. after finding the one factor, finding the rest turns out to be finding the factors of a quadratic.

    take the first factor and divide:

    x^3 - x^2 - 5x - 3 \div x + 1 = x^2 - 2x - 3

    \Rightarrow x^3 - x^2 - 5x - 3 = (x + 1) \left( x^2 - 2x - 3 \right)

    now factor the quadratic:

    \Rightarrow x^3 - x^2 - 5x - 3 = (x + 1)(x - 3)(x  + 1) = (x + 1)^2 (x - 3)
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  3. #3
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    thanks =) i actually got that answer but for some reason it doesnt foil out to the original equation =x maybe doing math @ 2 in the morning after physics and chemistry is not a good idea. Thanks alot though
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ffezz View Post
    maybe doing math @ 2 in the morning after physics and chemistry is not a good idea. Thanks alot though
    nope, not a good idea. but sometimes you have to do what you have to do. like me, for instance, i have to pull an all-nighter tonight

    you're welcome. good luck
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  5. #5
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    good luck =) il probably be back more in the future when i take calculus next semester lol
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