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Problem involving Power-Reducing Formula

  1. Apr 28, 2012 #1
    1. The problem statement, all variables and given/known data
    25zi9mr.png


    2. Relevant equations
    How in the world did they get their solution? Where did 27/8 come from?


    3. The attempt at a solution
    I did the arithmetic with the fractions inside before distributing the 9, and ended up getting something like -9/4 cos2x + 9/4 cos4x. Completely different from theirs.
     
  2. jcsd
  3. Apr 28, 2012 #2
    In the step above that, you have 1/4 + 1/8 = 2/8 + 1/8 = 3/8, then times 9 is 27/8
     
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