- #1

- 392

- 13

## Homework Statement

What is ##cos(\frac{2\pi}{7})+cos(\frac{4\pi}{7})+cos(\frac{6\pi}{7})## ?

## Homework Equations

Trigonometry

## The Attempt at a Solution

[/B]

I remember that the answer is ##-\frac{1}{2}##

But, I don't know how to do it since the angle is not nice. Any hint?