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For vectors a, b with |a| = |b| = 1 and a · b = 1/2, angle:

Aπ/6
Bπ/4
Cπ/2
Dπ/3 (60°; cos θ = 1/2)
Answer & Solution
Correct answer: D. π/3 (60°; cos θ = 1/2)
a · b = |a||b| cos θ. We have 1/2 = 1 × 1 × cos θ → cos θ. That is 1/2 = 1/2 → θ. So 1/2 = π/3 (60°).
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