If cos θ = −1/2 and θ ∈ (π, 3π/2), then θ equals:

Question

Accepted Answer

D. 4π/3

1. cos θ = −1/2 at θ = 2π/3 and θ = 4π/3 (within [0, 2π]).
2. We need θ in the third quadrant (π, 3π/2).
3. 4π/3 ≈ 240° lies in (180°, 270°), so θ = 4π/3.
_Source: syllabus Maths Ch 3 §3.5 (specific solutions)_

Answer

2π/3

Answer

π

Answer

5π/3

If cos θ = −1/2 and θ ∈ (π, 3π/2), then θ equals:

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