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WAEC Further Mathematics 2007 Question 36

Question 36

Vectors

Given that R = (4, 180°) and S = (3, 300°), find the dot product R.S.

  1. A.−6√3
  2. B.−6
  3. C.6
  4. D.6√3
Show the answer and explanation

Answer: B (−6)

Explanation

The angle between the vectors is 300° − 180° = 120°, so R·S = 4 × 3 × cos 120° = 12 × (−½) = −6.