Integral over 2 pi of Cosine of n x

Theorem
Let $m \in \Z$ be an integer.

Then:


 * $\ds \int_\alpha^{\alpha + 2 \pi} \cos m x \rd x = \begin {cases} 0 & : m \ne 0 \\ 2 \pi & : m = 0 \end {cases}$

Proof
Let $m \ne 0$.

Let $m = 0$.