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Math Help - Expressing sin(2x)sin(x) as a sum or difference of sin/cos terms

  1. #1
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    Expressing sin(2x)sin(x) as a sum or difference of sin/cos terms

    This site is excellent its really helping me understand the problems I am having.

    Anyway my latest problem is:

    Express sin(2x)sin(x) as a sum or difference of sin/cos terms.

    Can anyone help me?
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  2. #2
    MHF Contributor
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    Quote Originally Posted by JQ2009 View Post
    This site is excellent its really helping me understand the problems I am having.

    Anyway my latest problem is:

    Express sin(2x)sin(x) as a sum or difference of sin/cos terms.

    Can anyone help me?
    HI

    \sin 2x\sin x=(2\sin x\cos x)\sin x

    =2\sin^2 x\cos x

    =2(1-\cos^2 x)(\cos x)

     <br />
=2\cos x-2\cos^3 x<br />
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  3. #3
    Member
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    New Delhi
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    Express sin(2x)sin(x) as a sum or difference of sin/cos terms.
     as\ we\ know\ that\ \boxed{2 \sin C \sin D =  \cos(C-D) - \cos(C+D) }

     therefore\ \sin 2x \sin x = \frac{1}{2} \{ \cos(2x-x) - \cos(2x+x) \}
     \sin 2x \sin x = \frac{1}{2} \{ \cos x - \cos 3x \}
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