Question

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

Answer 1

Solve trig equatiom.

Ans: `+- pi/4`

Explanation:

Apply the trig identity; cos (a + b) = cos a.cos b - sin a.sin b
We get:
`cos (2x + x) = cos 3x = sqrt2/2`
Trig table of special arcs gives -->
`cos 3x = sqrt2/2` --> `arc x = +-pi/4`