Given a geometric progression with first term and common ratio

MATHEMATICS · Single correct · CBSE · Mathematics · Sequences and Series · Sequences and Series

Problem

Given a geometric progression with first term

a

and common ratio

r

, the sum of its first two terms is

30

and the sum of its first four terms is

120

. After eliminating

a

, which one of the following equations in

r

must be satisfied? (a)

1+r^{2}=4

(b)

1+r+r^{2}+r^{3}=4(1+r)

(c)

1+r+r^{2}=4(1+r)

(d)

1+r+r^{2}+r^{3}=4r