Answer:
π/4, 7π/4
Explanation:
You want the values of θ in the range 0 ≤ θ ≤ 2π such that cos(θ) = √2/2.
Cosine
The cosine function has the value √2/2 for angles ±45° = ±π/4 radians and those angles added to an integer multiple of 2π. In the domain of interest, the angles are ...
θ = π/4 and 7π/4