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Homework Help: Trigonometry problem

  1. Aug 15, 2011 #1
    This is not homework question, just curious about it though. This problem is supposed to be done without a computing device and was in an exam at a university course. I don't think it can be done.

    1. The problem statement, all variables and given/known data
    I want to find the maximum of this function:

    Y = sin(x) + sin(2x)

    2. Relevant equations

    3. The attempt at a solution

    Attempted sin(2x) = 2sinx*cosx, tried to draw it, tried to go euler's formula, no luck whatsoever (of course I take the derivative!)

    Mathematica gives me this:

    FindMaximum[Sin[x] + Sin[2*x], {x, 0}]

    Out[1]= {1.76017, {x -> 0.935929}}

    Any ideas? It really seems simple, but I just can't figure it out...

  2. jcsd
  3. Aug 15, 2011 #2


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    Homework Helper

    Why don't you just solve dy/dx = 0 and then sub cos(2x) as 2cos2-1 ?

    You should get a quadratic in cosx to solve.
  4. Aug 16, 2011 #3
    Lol where is my mind! Thanks :P
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