Which of the following expressions represents the sum of the first terms of a…

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

Problem

Which of the following expressions represents the sum

S_n

of the first

n

terms of a geometric progression whose first term is

a

and common ratio is

r\,(r\neq1)

? (a)

S_n=\dfrac{a(r^{n}-1)}{r}

(b)

S_n=\dfrac{a(1-r^{n})}{1-r}

(c)

S_n=a\,r^{n-1}

(d)

S_n=\dfrac{a(r^{n}-1)}{1-r}