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Homework Help: Identities simplify expression

  1. Dec 12, 2009 #1
    I have been trying to do this problem for a long time, and still can not do it. I know the answer is sin2x, but I have no idea how to do it:

    write expression as sine, cosine, or tangent of an angle

    sin3xcosx - cos3xsinx

    THANKS!
     
  2. jcsd
  3. Dec 12, 2009 #2

    Dick

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    Homework Helper

    Use the sine addition formula, sin(a-b)=sin(a)cos(b)-cos(a)sin(b). Line that up with your expression and figure out what a and b should be.
     
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