# Sum of squares of cosine.

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• February 26th 2011, 10:25 AM
arm
Sum of squares of cosine.
Find: $cos ^{2}(\frac{\pi }{5})+ cos^{2} (\frac{2\pi }{15})+ cos^{2} (\frac{8\pi }{15})$
• February 26th 2011, 12:56 PM
mr fantastic
Quote:

Originally Posted by arm
Find: $cos ^{2}(\frac{\pi }{5})+ cos^{2} (\frac{2\pi }{15})+ cos^{2} (\frac{8\pi }{15})$

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