Find: $\displaystyle cos ^{2}(\frac{\pi }{5})+ cos^{2} (\frac{2\pi }{15})+ cos^{2} (\frac{8\pi }{15})$
Last edited by mr fantastic; Feb 26th 2011 at 12:56 PM. Reason: Re-titled.
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Originally Posted by arm Find: $\displaystyle cos ^{2}(\frac{\pi }{5})+ cos^{2} (\frac{2\pi }{15})+ cos^{2} (\frac{8\pi }{15})$ To get help you need to show some effort. Show your work and say where you're stuck.
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