Question

How do you find the exact value of `arccos (-1/2)`?

Answer 1

`(2pi)/3 + 2kpi`
`(4pi)/3 + 2kpi`

Explanation:

Trig table and unit circle -->
`cos x = - 1/2` --> arc `x = +- (2pi)/3`
The arc `(-2pi)/3` is co-terminal to `(4pi)/3`.
General answers:
`(2pi)/3 + 2kpi`
`(4pi)/3 + 2kpi`