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Math Help - trigonometry (compound angles)

  1. #1
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    trigonometry (compound angles)

    hi , im stuck with this final question.

    sin(A+B)sin(A-B) = sin^2A - sin2^2B


    thank you ..
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  2. #2
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    Quote Originally Posted by mike--1988 View Post
    hi , im stuck with this final question.

    sin(A+B)sin(A-B) = sin^2A - sin2^2B


    thank you ..
    \sin(a+b)\sin(a-b) =

    (\sin{a}\cos{b}+\cos{a}\sin{b})(\sin{a}\cos{b}-\cos{a}\sin{b}) =

    \sin^2{a}\cos^2{b} - \cos^2{a}\sin^2{b} =

    \sin^2{a}(1 - \sin^2{b}) - (1 - \sin^2{a})\sin^2{b} =

    finish ...
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