Question

How do I solve `cos x= (sqrt 2/2)` for `-2pi <=x<=2pi`?

Answer 1

`-(7pi)/4; -pi/4; pi/4; (7pi)/4`

Explanation:

`cos x = sqrt2/2`
Trig table and unit circle give 2 solutions:
`x = +- pi/4`
In the interval `(0, 2pi)`, the answers are:
`x = pi/4`, and
`x = (7pi)/4` (co-terminal to `-pi/4`)
In the interval `(-2pi, 0)` the 2 answers are:
`x = - pi/4`, and
`x = - (7pi)/4` (co-terminal to `pi/4`)