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WAEC Further Mathematics 2024 Question 30

Question 30

Trigonometry

In triangle XYZ, |XY| = 10, |YZ| = 9 cm and |XZ| = 7 cm. If angle XYZ = α, find the value of cos α.

  1. A.11/15
  2. B.17/35
  3. C.5/21
  4. D.7/32
Show the answer and explanation

Answer: A (11/15)

Explanation

Angle XYZ is at Y, between XY and YZ, opposite XZ. Cosine rule: cos α = (10² + 9² − 7²)/(2 × 10 × 9) = 132/180 = 11/15.