# Sum of squares of cosine.

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