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Derivative of A Trigonometric Function

  1. Feb 27, 2012 #1
    1. The problem statement, all variables and given/known data
    Find the derivative of f(x) = 1/4 sin^2 2x


    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    f'(x) =1/4(sin 2x)^2

    f'(x) = 1/4*2(sin 2x)(cos 2x)

    f'(x) = 1/4(sin 4x)

    That is my answer to the problem, but the book has it as f'(x) = 1/2(sin 4x)
    What did I do wrong?
     
  2. jcsd
  3. Feb 27, 2012 #2

    lanedance

    User Avatar
    Homework Helper

    you forgot the factor of 2 when you differentiate (sin(2x))
     
  4. Feb 27, 2012 #3
    Oh, yes, thank you.
     
  5. Feb 27, 2012 #4

    Mark44

    Staff: Mentor

    (Above) This is f(x), not f'(x).
     
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