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Math Help - chain rule derivatives...

  1. #1
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    chain rule derivatives...

    y() = e sin(8)

    for this one i got 8e^(theta)*cos(8theta)...

    but it was wrong, what did i do wrong??
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  2. #2
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    You have neglected the fact that there is a product of functions.

    If f(x) = g(x)*h(x), then f'(x) = g(x)*h'(x) + g'(x)*h(x).

    Ringing any bells?
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  3. #3
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    Quote Originally Posted by TKHunny View Post
    You have neglected the fact that there is a product of functions.

    If f(x) = g(x)*h(x), then f'(x) = g(x)*h'(x) + g'(x)*h(x).

    Ringing any bells?
    can you do it for me so i can see...
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  4. #4
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    Hello, mathaction!

    Have you forgotten the Product Rule?


    y \:=\:e^{\theta}\!\cdot\!\sin(8\theta)

    We have: . \frac{dy}{d\theta} \;=\;e^{\theta}\cdot\cos(8\theta)\cdot8 + e^{\theta}\cdot\sin(\theta) \;=\;e^{\theta}\left[8\cos(8\theta) + \sin(\theta)\right]

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