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Math Help - please fix it.

  1. #1
    Member srirahulan's Avatar
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    Lightbulb please fix it.

    sinAsin(A+2B)-sinBsin(B+2A)=sin(A+B)sin(A-B) please prove this.
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  2. #2
    MHF Contributor
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    Re: please fix it.

    Just use repeatedly on both sides formulas for sin(x + y), sin(2x) and cos(2x).
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  3. #3
    Member srirahulan's Avatar
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    Re: please fix it.

    I can't understand.
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  4. #4
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    Re: please fix it.

    The left-hand side contains sin(A + 2B). Use the formula sin(x + y) = sin(x)cos(y) + cos(x)sin(y) to replace sin(A + 2B). The right-hand side contains sin(A - B). Use the formula sin(x - y) = sin(x)cos(y) - cos(x)sin(y) to replace sin(A - B). Keep using these formulas along with sin(2x) = 2sin(x)cos(x) and cos(2x) = cos^2(x) - sin^2(x) until you have no longer sine or cosine of a sum of angles or a double angle.
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