# Sum of cosines #2

• Feb 26th 2011, 11:21 AM
arm
Sum of cosines #2
Find: $cos (\frac{2\pi }{15}) + cos (\frac{4\pi }{15}) +...+ cos (\frac{14\pi }{15})$
• Feb 26th 2011, 01:58 PM
mr fantastic
Quote:

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

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