Respuesta :

Answer:

Step-by-step explanation:

cos(2θ) - cosθ + 1 = 0

2cos²θ - 1 - cosθ + 1 = 0

2cos²θ - cosθ = 0

2cosθ(cosθ - 1/2) = 0

cosθ = 0, θ = π/2, 3π/2

cosθ = 1/2, θ = π/3. 5π/3

So answer is 3rd choice