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Homework Help: Calc BC derivative problem with trig and double angle -- Help please

  1. Oct 5, 2015 #1
    1. The problem statement, all variables and given/known data
    Find f'(x) if f(x) = 8^(sin^2(3x))
    Hint: you will need to use the double angle formula for trig functions and your answer should only have one trig function in it.

    2. Relevant equations
    if y=a^u then y' = ln a * a^u * du
    sin(2x) = 2sinxcosx

    3. The attempt at a solution
    We're only on the second chapter so I'm not sure if we really need the first equation I gave, which is from the fifth chapter (but I'm in BC so maybe she expects us to know it already?). Still, using that equation I got f'(x) = ln 8 * 8^(sin^2(3x)) * 3sin6x

    The 3sin6x came from when I took the derivative of sin^2(3x) and converted it from 6sin3xcos3x to 3sin6x

    But I don't know how my teacher (an online teacher) wanted the answer to only have one trig function? Did I mess up somewhere?
  2. jcsd
  3. Oct 5, 2015 #2
    In terms of sin2θ, cos(2θ)=??
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