The magnitude of vector u is 34, and the magnitude of vector v is 20. The dot product u · v = –10. What is the approximate angle between the vectors?

Use the dot product formula u · v = |u||v| cos θ. Thus cos θ = −10/(34 × 20) ≈ −0.0147, so θ ≈ cos⁻¹(−0.0147) ≈ 90.8°, which rounds to 91°, choice C.

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