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Math Help - Next step on proving an identity.

  1. #1
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    Next step on proving an identity.

    Hello. I'm trying to prove:

    cot(\frac{A}{2}) - tan(\frac{A}{2}) = 2 cot (A)

    So far, this is what I've done:

    cot(\frac{A}{2}) - tan(\frac{A}{2}) = \dfrac{1+cos(A)+cos(A)+cos^2(A)-sin^2(A)}{sin(A)(1+cos(A))}

    If it weren't for the pesky cos^2(A)-sin^2(A), I could simplify the numerator pretty easily. However, that not being the case, I'm not sure what the next step is.

    Thanks.
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  2. #2
    MHF Contributor Also sprach Zarathustra's Avatar
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    1+2cos(a)+cos^2(a)-(1-cos^2(a))=2cos(a)+2cos^2(a)=...
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  3. #3
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    Thanks, that got me where I needed to go!
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