# Thread: Sum of cosines #2

1. ## Sum of cosines #2

Find: $cos (\frac{2\pi }{15}) + cos (\frac{4\pi }{15}) +...+ cos (\frac{14\pi }{15})$

2. Originally Posted by arm
Find: $cos (\frac{2\pi }{15}) + cos (\frac{4\pi }{15}) +...+ cos (\frac{14\pi }{15})$
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