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Math Help - college algebra help

  1. #1
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    college algebra help

    i dont how to do this and i can't figure it out

    Determine the x values where F(x) is positive

    f(x)=x^(3)-9x


    determine the x values where f(x) is increasing

    f(x)=x^(2)-2x-8
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  2. #2
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    Quote Originally Posted by ducktrix View Post
    Determine the x values where F(x) is positive

    f(x)=x^3-9x
    Hi ducktrix,

    Welcome to MHF!

    In the future please post one problem per thread and show all attempted work so we know what you know.

    For #1, first factor this. x^3-9x=x(x^2-9)=x(x+3)(x-3)

    You should be able to tell that the three zeros of f(x) are 0, 3 and -3. So draw a number line and mark these three points on it. Now the regions inbetween these values will either be positive or negative. Choose a test point to see. Make sense?
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