Q. If $S$ is the sum of an infinite GP, the first term $a$, then the common ratio $r$ is given by
A) $\frac{a - S}{S}$
B) $\frac{S - a}{S}$
C) $\frac{a}{1 - S}$
D) $\frac{S - a}{a}$
Explanation
(b)
Sum of an infinite GP = $\frac{a}{1 - r} = S$
$\Rightarrow \ a = S(1 - r)\ \Rightarrow \ r = \frac{S - a}{S}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.