Question

How do you solve `cos2x=1/sqrt2`?

Answer 1

`pi/8 + 2kpi`
(15pi)/8 + 2kpi

Explanation:

Trig table of special arcs, and unit circle -->
`cos 2x = 1/sqrt2 = sqrt2/2` -->
`2x = +- pi/4`
`x = +- pi/8`
General answers:
`x = pi/8 + 2kpi`
`x = - pi/8`, or `x = (15pi)/8 + 2kpi` --> (co-terminal)