Final answer:
The correct values of θ such that cos(θ) = -1/2 are 2π/3 (Option B) and 4π/3 (Option C), corresponding to the second and third quadrants on the unit circle where the cosine function has negative values.
Step-by-step explanation:
To find all values of θ such that cos(θ) = -1/2, we need to look at where the cosine function reaches the value of -1/2 on the unit circle. The cosine function gives us the x-coordinate of a point on the unit circle, and it has the value of -1/2 at specific standard angles in the second and third quadrants, namely at θ = 2π/3 and θ = 4π/3.
Option A, θ = π/3, refers to the first quadrant where all trigonometric functions are positive, so it cannot be correct. Option B, θ = 2π/3, is in the second quadrant where cosine is negative, hence this option is correct. Option C, θ = 4π/3, falls in the third quadrant, which also has a negative cosine value, making it correct as well. Lastly, Option D, θ = 5π/3, is in the fourth quadrant where cosine is positive, so this option is not correct. Therefore, the correct values of θ are 2π/3 and 4π/3.