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Math Help - X^3-9x Graphing. Finding xints/yints, cps, ips

  1. #1
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    X^3-9x Graphing. Finding xints/yints, cps, ips

    I have this problem that seems relatively easy but i seem to be messing up somewhere.

    First i find x-ints/y-ints
    x^3-9x
    x(x+3)(x-3)
    x=0 x=3 x=-3
    y=0

    Now the troubling part
    Critical Point: F'(x)=0
    3x^2-9=0

    I use simple quadratic formula and get x values of 18 and -18 (these values don't seem correct) i can't seem to find out what i am doing wrong, any help on this is greatly appreciated.
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  2. #2
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    Quote Originally Posted by Spily View Post
    I have this problem that seems relatively easy but i seem to be messing up somewhere.

    First i find x-ints/y-ints
    x^3-9x
    x(x+3)(x-3)
    x=0 x=3 x=-3
    y=0

    Now the troubling part
    Critical Point: F'(x)=0
    3x^2-9=0

    I use simple quadratic formula and get x values of 18 and -18 (these values don't seem correct) i can't seem to find out what i am doing wrong, any help on this is greatly appreciated.
    3x^2-9=0\rightarrow x^2=3\rightarrow x=\pm\sqrt{3}
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