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Math Help - Sum of cosines #2

  1. #1
    arm
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    Sum of cosines #2

    Find: cos (\frac{2\pi }{15}) + cos (\frac{4\pi }{15}) +...+ cos (\frac{14\pi }{15})
    Last edited by mr fantastic; February 26th 2011 at 12:58 PM. Reason: Re-titled.
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  2. #2
    Flow Master
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    Quote Originally Posted by arm View Post
    Find: cos (\frac{2\pi }{15}) + cos (\frac{4\pi }{15}) +...+ cos (\frac{14\pi }{15})
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