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

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

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- Apr 8th 2009, 04:20 AMsaiyanmx89another ratio test
$\displaystyle \sum^ \infty_{n=1} \frac{1}{n}cosn\pi$

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 AMmr fantastic
Use the alternating series test: Alternating series test - Wikipedia, the free encyclopedia