GATE 2019 BT – Question 23

Engineering Mathematics · Calculus: Sequences and series, tests for convergence · 1 mark · Multiple choice

Which sequences are geometric?

P: 1,6,11,16,21,26,…
Q: 9,6,3,0,−3,−6,…
R: 1,3,9,27,81,…
S: 4,−8,16,−32,64,…

P and Q only
R and S only
Q and S only
P, Q and R only

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Show answer and explanation

Correct answer: (B) R and S only

Explanation

Geometric sequences have a constant ratio of consecutive terms. R has ratio 3 and S ratio −2. P and Q instead have constant differences, 5 and −3, and their ratios vary. Hence R and S only, B.

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