If cos θ = −1/2 and θ ∈ (π, 3π/2), then θ equals:
A2π/3
Bπ
C5π/3
D4π/3
Answer & Solution
Correct 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: NCERT Class 11 Maths Ch 3 §3.5 (specific solutions)_
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