Evaluate ∑k=0n−1cos(2kπn+α)\sum_{k=0}^{n-1} \cos\left(\frac{2k\pi}{n} + \alpha\right)∑k=0n−1cos(n2kπ+α) for n>1n > 1n>1.
ncosαn\cos\alphancosα
000
111
nsinαn\sin\alphansinα