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Math Help - Please help proving this identity

  1. #1
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    Please help proving this identity

    (cos x - siny)/ (cosy - sinx) = (cosy + sinx)/(cosx+siny)

    - Thanks for the help
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  2. #2
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    Write sines in terms of cosines, meaning if you have sin x write cos(pi/2 - x).
    Then use the sine and cosine sum/difference formulas.
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  3. #3
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    Quote Originally Posted by ThePerfectHacker View Post
    Write sines in terms of cosines, meaning if you have sin x write cos(pi/2 - x).
    Then use the sine and cosine sum/difference formulas.

    this might be a stupid question, but if you use the sum/difference formula on
    cos (2/pi-x) wont you just be back at sin x?
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