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Math Help - Calculus Interval Math Problem

  1. #1
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    Calculus Interval Math Problem

    Find all intervals for which the graph of the function y=(8x^3) - (2x^4) is concave downward.
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  2. #2
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    Concavity is test with the second derivative test.

    What is the 2nd derivative of y?

    The first is y'=24x^2-8x^3

    Once you have the second derivative, set y''=0 to obtain the inflection points.

    Spoiler:
    y''=48x-24x^2=0\Rightarrow 24x(2-x)=0\Rightarrow x=0,2

    What does this tell you now?
    Last edited by dwsmith; December 17th 2010 at 06:41 PM.
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