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WAEC Further Mathematics 2007 Question 14

Question 14

Vectors

Two vectors m and n are defined by m = 3i + 4j and n = 2i − j. Find the angle between m and n.

  1. A.97.9°
  2. B.79.7°
  3. C.63.4°
  4. D.36.4°
Show the answer and explanation

Answer: B (79.7°)

Explanation

m·n = 6 − 4 = 2, |m| = 5, |n| = √5. cos θ = 2/(5√5) ≈ 0.1789, so θ ≈ 79.7°.