Question

How do you solve `cos 2x = 1`?

Answer 1

Another way:

`cos 2x = 2.cos^2 x - 1 = 1`
`cos^2 x = 1`
cos x = 1 -> x = 0 and x = 2pi
cos x = -1 -> x = pi.
Check:
x = pi -> 2x = 2pi -> cos 2x = 1 -> 1 = 1 Correct.