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Math Help - derivative of trig function

  1. #1
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    derivative of trig function

    I cannot seem to come up with a correct answer for this:

    Find the derivative of f when

    f(x)= 3 tan 4x cos^3 4x

    The answer choices are all in sin and cos, and I seem to keep getting an answer as a fraction, but that is not a choice in any answer. Any help/advice would be greatly appreciated. Thx!
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by calcnewbie View Post
    I cannot seem to come up with a correct answer for this:

    Find the derivative of f when

    f(x)= 3 tan 4x cos^3 4x

    The answer choices are all in sin and cos, and I seem to keep getting an answer as a fraction, but that is not a choice in any answer. Any help/advice would be greatly appreciated. Thx!
    if all the answers are in sines and cosines then switch to sines and cosines

    f(x) = 3 \tan 4x \cos^3 4x = 3 \frac {\sin 4x}{\cos 4x} \cdot \cos^3 4x = 3 \sin 4x \cos^2 4x

    we could change this to purely sines, but since cosines are in the answer, lets not do that

    now use the product rule (and the chain rule) to find the derivative
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  3. #3
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    Ok I'll give it a shot. Thx!
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