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WAEC Further Mathematics 2020 Question 15

Question 15

Trigonometry

If sin X = 3/5 and cos Y = 24/25 where X and Y are acute, Find the value of cos (X + Y).

  1. A.117/125
  2. B.24/25
  3. C.3/5
  4. D.7/25
Show the answer and explanation

Answer: C (3/5)

Explanation

cos X = 4/5 and sin Y = 7/25. cos(X + Y) = (4/5)(24/25) − (3/5)(7/25) = 96/125 − 21/125 = 75/125 = 3/5.