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Math Help - derivatives

  1. #1
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    derivatives

    my question is write down the derivatives of the following

    F(x) =x^7 and g(x) = cos(4x)

    For these I got

    f'(x)=7x^6 and g'(x) -4 cos(4x)

    Is this correct.

    The second part says differentiate the function using the product rule.

    This bit I am confused

    Please help
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  2. #2
    Super Member wingless's Avatar
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    g(x) = \cos 4x

    g'(x) is not -4\cos4x
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  3. #3
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    can you show me where i have gone wrong
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  4. #4
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    Quote Originally Posted by tracy207 View Post
    can you show me where i have gone wrong
    g(x) = cos(4x)
    Use the chain rule to find the derivative of g(x)
    g'(x) = 4 ( -sin (4x) )= -4sin(4x)
    You have to take the derivative of 4x and then take the derivative of the function cosine. I don't see why you need to use product rule here. May be you didn't write the entire question here.
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