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JAMB Mathematics 1985 Question 26

Question 26

Trigonometry

In ΔXYZ, XY = 13cm, YZ = 9cm, XZ = 11cm and XYZ = θ°. Find cos θ°

  1. A.4/39
  2. B.43/39
  3. C.209/286
  4. D.−1/6
  5. E.43/78.
Show the answer and explanation

Answer: E (43/78.)

Explanation

By the cosine rule, cos θ = (13² + 9² − 11²)/(2 × 13 × 9) = 129/234 = 43/78.