1. ## complex variables

Prove that

$\displaystyle \sum$sin(k$\displaystyle \theta$)= [sin(n$\displaystyle \theta$/2)sin((n+1)$\displaystyle \theta$/2)]/sin$\displaystyle \theta$/2)

2. Originally Posted by LCopper2010
Prove that

$\displaystyle \sum$sin(k$\displaystyle \theta$)= [sin(n$\displaystyle \theta$/2)sin((n+1)$\displaystyle \theta$/2)]/sin$\displaystyle \theta$/2)
Easy way? $\displaystyle \sum_{k}\sin(k\theta)=\sum_{k}\Im\left(e^{ik\theta }\right)$

3. ## more help

I still don't really understand...could you elaborate a bit? Thanks!

4. Originally Posted by LCopper2010
I still don't really understand...could you elaborate a bit? Thanks!
I'm not going to tell you the answer, but maybe a helpful hint is in order. Remember the geometric sum formula.