1. another ratio test

$\sum^ \infty_{n=1} \frac{1}{n}cosn\pi$

I know that the cosn(\pi) becomes (-1)^n, but what do I do with the (1/n) according nth term test?

2. Originally Posted by saiyanmx89
$\sum^ \infty_{n=1} \frac{1}{n}cosn\pi$

I know that the cosn(\pi) becomes (-1)^n, but what do I do with the (1/n) according nth term test?
Use the alternating series test: Alternating series test - Wikipedia, the free encyclopedia