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JAMB Mathematics 1993 Question 23

Question 23

Progressions

If k + 1, 2k − 1, 3k + 1 are three consecutive terms of geometric progression, find the possible values of the common ratio.

  1. A.0, 8
  2. B.1, 5/3
  3. C.2, 3
  4. D.1, 1
Show the answer and explanation

Answer: B (1, 5/3)

Explanation

For a GP, (2k − 1)² = (k + 1)(3k + 1), which gives k² − 8k = 0, so k = 0 or 8. k = 0 gives 1, −1, 1 (ratio −1) and k = 8 gives 9, 15, 25 (ratio 5/3).