Can anyone tell me what is the sum of a finite series of Sines.(adsbygoogle = window.adsbygoogle || []).push({});

[tex]\sum_{n=1}^N \sin^2 (n \phi) [/tex]. I am going through a text and it gives it as (N+1)/2. I tried to derive it. The N comes out ok when you use the half angle identity but I can't figure out a general rule for the Cosines that appear

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# Sum of a finite sine series

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