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October 8th, 2010, 07:14 PM   #1
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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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