(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

(Sorry, but I haven't mastered using the sigma notation in these forums yet).

Find the sum of the following infinite series: (n=0)^(inf) SIGMA ((pi)cos(n))/(5^n).

2. Relevant equations

I tried using the formula S=(a_{1})/(1-r).

I know that a=pi, but I can't find "r." The equation doesn't have a consistent rate. Should I be using a different method?

Thanks.

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# Homework Help: Sum of an Infinite Series

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