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Thread: Help Proving double-angle identities

  1. July 20th 2007, 11:36 PM #1
    fam600
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    Help Proving double-angle identities

    Can someone prove this for me, please show enough steps so that i know what your doing along the way. Thanks

    sin3x=3sinx-4sin^3x - the x isn't with ^3.
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  2. July 21st 2007, 12:20 AM #2
    red_dog
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    \sin 3x=\sin (2x+x) and use the formula
    \sin(a+b)=\sin a\cos b+\sin b\cos a
    and \sin 2x=2\sin x\cos x, \ \cos 2x=1-2\sin^2x
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