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Math Help - Trig Identity

  1. #1
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    Exclamation Trig Identity

    I need help with proving this trig identity. I tried doing it out but I'm not sure if I'm doing it right since it's getting so expanded. Is there any other way to do it than making the cos4x = cos(2x + 2x) = cos2xcos2x-sin2xsin2x = ...?

    Here's the identity:

    \frac{\cos4x + \cos2x}{\sin4x + \sin2x} = \cot3x
    Last edited by 83457; December 19th 2009 at 10:07 AM.
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  2. #2
    MHF Contributor red_dog's Avatar
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    Use the identities

    \cos\alpha+\cos\beta=2\cos\frac{\alpha+\beta}{2}\c  os\frac{\alpha-\beta}{2}

    \sin\alpha+\sin\beta=2\sin\frac{\alpha+\beta}{2}\c  os\frac{\alpha-\beta}{2}
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