Question

How do you find all solutions if 0 ≤ θ < 2π for `cos 2x = sqrt2/2`?

Answer 1

`pi/8; (7pi)/8`

Explanation:

`cos 2x = sqrt2/2`
Trig table and unit circle give 2 solutions:
`2x = +- pi/4`
a. `2x = pi/4` -->
`x = pi/8`
b. `2x = - pi/4`, or `2x = (7pi)/4` --> (co-terminal)
`x = (7pi)/8`