Geometric series problem

[ashen hazel]

How would I be able to evaluate this?

[wicked atlas]

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[foggy steeple]

just evaluate each term, and sum them

$\cos(0)+\cos(\pi/4)+\cos(\pi/2)+\cos(3\pi/4)+\cos(\pi)$

[grand pier]

Omegabet_

[ashen hazel]

I see thanks

+close