Q. The sum to infinity of the progression $9 - 3 + 1 - \frac{1}{3} + ...$ is
A) 9
B) 9⁄2
C) 27⁄4
D) 15⁄2
Explanation
(c)
Given series is $9 - 3 + 1 - \frac{1}{3} + ...\infty$
This is an infinite GP series.
$\therefore\ S_{\infty} = \frac{a}{1 - r} = \frac{9}{1 - \left( - \frac{1}{3} \right)} = \frac{27}{4}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.