By using the complex representations of sine and cosine, show that $$\sum_{m=0}^n\sin m\theta =\frac{\sin\frac{n}{2}\theta\sin\frac{n+1}{2}\theta}{\sin\frac{1}{2}\theta}$$
So I am not too sure how to go about this proof. I tried to substitute sine for its complex representation but I can't see how to evaluate the sum?
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