Question

How do you evaluate cos(2π/3)?

Answer 1

`-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.