Respuesta :

Answer:

Step-by-step explanation:

2cos²θ - 1 - cosθ = 0

(2cosθ + 1)(cosθ - 1) = 0

cosθ = -1/2, θ = 2π/3, 4π/3

cosθ = 1, θ = 0

so answer is 3rd choice

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