How do you evaluate cos(2π/3)?

1 Answer
Nov 5, 2015

-1/2

Explanation:

This is easy if you know basic angles with radians and the basic values of cosine.

pi = 180 degrees
2pi = 180 * 2 degrees = 360 degrees
(2pi)/3 = (360 degrees)/3 = 120 degrees

If you know the unit circle, you know that cos(120) is the opposite of cos(60) (both in degrees). This is because they are in different quadrants.

Since cos(60) = 1/2
cos(120) = -1/2

PM me if you don't know how the unit circle works :-).
Hope this helped.