$$\sum_{i=1}^N \frac{1}{\sin^2(\frac{i \pi}{2 N})} = \frac{1}{3}(2N^2+1)$$
How can I prove this ?
Thank you.
2026-03-27 10:13:00.1774606380
How can I prove this ? $\sum\limits_{i=1}^N \frac{1}{\sin^2(\frac{i \pi}{2 N})} = \frac{1}{3}(2N^2+1)$
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