# Thread: sum of cos terms

1. ## sum of cos terms

How to find sigma(summation) n from -N to N for the exp
cos2(4n+60)?
Thank you

$\displaystyle \sum_{n = -N}^N{\cos{[2(4n+60)]}}$?

3. Originally Posted by Prove It

$\displaystyle \sum_{n = -N}^N{\cos{[2(4n+60)]}}$?

Or maybe:

$\displaystyle \sum_{n = -N}^N{e^{\cos^2{(4n+60)}}}
$

4. According to a pm from vikrant, Prove It has the correct formula to be evaluated, I believe. So, what's desired is

$\displaystyle\sum_{n=-N}^{N}\cos(8n+120).$

I am not qualified to answer this question (other than simply asking Mathematica to spit out the answer, which it does), so someone else please continue.