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Math Help - Chain Rule Question.

  1. #1
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    Chain Rule Question.

    Find \frac{dy}{dx} given that y=\frac{u-17}{u+17} , u=x^3.

    I began trying to solve it like this: \frac{dy}{du} = \frac{(u+17)(-17)-(u-17)(17)}{(u+17)^2} = \frac{-34u}{(u+17)^2}

    \frac{du}{dx} = 3x^2

    \frac{dy}{dx} = \frac{-34x^3}{(x^3+17)^2} (3x^2) = \frac{-102x^5}{(x^3+17)^2}

    Can someone tell me what I am doing wrong?
    Thanks
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  2. #2
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    Re: Chain Rule Question.

    (u+17)'=1, not 17.
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  3. #3
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    Re: Chain Rule Question.

    Thank you emakarov, sometimes I think I am blind.
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