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Math Help - Proving a trigonometric identity

  1. #1
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    Proving a trigonometric identity

    Hey guys! I'm new at MH!
    I'm doing a long exercise where I need to prove this identity that I obtained myself (it's a sort of conjecture). I'm stuck though! I tried developing what's inside the square root in the first member, but it didn't get anything useful by doing that.

    Could anybody help me or give me hints on how to approach it?

    Thank you very much!
    Attached Thumbnails Attached Thumbnails Proving a trigonometric identity-trig.png  
    Last edited by Phyba; October 28th 2012 at 05:47 PM.
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  2. #2
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    Re: Proving a trigonometric identity

    The -1 in the first member is out of the cos
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  3. #3
    MHF Contributor MarkFL's Avatar
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    Re: Proving a trigonometric identity

    Expand under the radical, apply a Pythagorean identity, then a double-angle identity for cosine.
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