# Complex analysis question (only need a hint)

1. Jan 18, 2005

### fresh

i know it's supposed to be a simple question. frustrating because it is not coming to me. just want a hint.

question is:
how do you write
1 + cos(theta) + cos (2*theta) + cos(3*theta).... cos(n*theta) using the fact that (z^(n+1) -1) / (z^(n) -1) = 1 + z + z^(2) +... + z^(n)

2. Jan 18, 2005

### dextercioby

$$Re \sum_{k=0}^{n} e^{ikz}$$