- #1
terryds
- 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?