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Math Help - For what intervals is the following function increasing and decreasing?

  1. #1
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    For what intervals is the following function increasing and decreasing?

    y= 3x^3 - 16x + 2

    a) increasing for x < -2.31 and x > 2.31; decreasing for -2.31 < x < 2.31
    b) increasing for -2.31 < x < 2.31; decreasing for x < -2.31 and x > 2.31
    c) increasing for x < - 4/3 and x > 4/3; decreasing for -4/3 < x < 4/3
    d) increasing for -4/3 < 4/3; decreasing for x < -4/3 and x > 4/3

    and what window did you use?
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  2. #2
    MHF Contributor
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    y'(x)=9x-16=(3x+4)(3x-4)
    You just have to find the sign of y'(x)
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