- #1

Dragonfall

- 1,030

- 4

## Homework Statement

[tex]\sum_{k=0}^{4}\cos^2\left({\frac{2\pi k}{5}\right) = 5/2[/tex]

## The Attempt at a Solution

I have to prove that. I don't know how. Maple gives

[tex]1+2*cos((2/5)*Pi)^2+2*cos((1/5)*Pi)^2[/tex]

evaluated numerically it is equal to 2.499999. But I don't remember the trick to doing this algebraically.