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JAMB Mathematics 1998 Question 20

Question 20

Progressions

The sum of the first three terms of a geometric progression is half its sum to infinity. Find the positive common ratio of the progression.

  1. A.1/4
  2. B.1/2
  3. C.1/∛3
  4. D.1/∛2
Show the answer and explanation

Answer: D (1/∛2)

Explanation

a(1 − r³)/(1 − r) = ½ × a/(1 − r), so 1 − r³ = ½, r³ = ½ and r = 1/∛2.