Find the value of the sum ∑k=0n−1cos(2kπn+α)\sum_{k=0}^{n-1} \cos\left(\frac{2k\pi}{n} + \alpha\right)∑k=0n−1cos(n2kπ+α).
ncosαn \cos \alphancosα
000
111
cos(nα)\cos(n\alpha)cos(nα)