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 October 8th, 2010, 07:14 PM #1 Newbie   Joined: Oct 2010 Posts: 1 Thanks: 0 A question about sine of multiple angles Today, when I'm following paper, I run into this equation $\displaystyle \frac{1}{N+1}\sum_{n=1}^{N} \frac{\sin^2 \frac{n\pi}{N+1}}{\cos \theta- \cos\frac{n\pi}{N+1}} = \frac{\sin[N\theta]}{\sin[ (N+1)\theta]}$ where N is a positive integer. This equation seems to be always satisfied, but I can't find a way to prove it. Could anybody help me? Last edited by skipjack; February 23rd, 2018 at 07:43 PM.

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