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WAEC Further Mathematics 2017 Question 18

Question 18

Trigonometry

Given that sin x = 5/13 and sin y = 8/17, where x and y are acute, find the value of cos (x + y).

  1. A.130/221
  2. B.140/221
  3. C.140/204
  4. D.220/23
Show the answer and explanation

Answer: B (140/221)

Explanation

cos x = 12/13, cos y = 15/17. cos(x + y) = 180/221 − 40/221 = 140/221.