Prove that for any real number [tex] \alpha \neq 0, \pm 2 \pi, \pm 4 \pi [/tex]. . . one has(adsbygoogle = window.adsbygoogle || []).push({});

[tex] \frac{1}{2} + \cos \alpha + . . . \cos N \alpha = \frac{sin[(N+\tfrac 1 {2}) \alpha ]}{ 2 \sin (\tfrac \alpha {2})} [/tex]

I know it involves Euler's formula that relates sin and cos to the exponential function, and the formula for the sum of a geometric series. I'm not sure how to start this simple proof. Any help with be great.

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# Homework Help: A proof

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