Which one of the following is the necessary and sufficient condition for the infinite…

MATHEMATICS · Single correct · A Level · Mathematics · Sequences and series · Sequences and series

Problem

Which one of the following is the necessary and sufficient condition for the infinite geometric series

a+ar+ar^{2}+\text{ }\dots

to have a finite sum? (a)

r<1

(b)

|r|<1

(c)

|r|\le 1

(d)

|r|>1