cos(2θ) + sin²(θ) = 0
Half-angle identity:
cos(2θ) + (1 - cos(2θ))/2 = 0
Simplify:
2 cos(2θ) + 1 - cos(2θ) = 0
cos(2θ) = -1
Solve for θ :
2θ = arccos(-1) + 2nπ
2θ = π + 2nπ
θ = π/2 + nπ
where n is any integer.
