# another ratio test

• Apr 8th 2009, 04:20 AM
saiyanmx89
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?
• Apr 8th 2009, 04:35 AM
mr fantastic
Quote:

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