### Home > PC3 > Chapter 12 > Lesson 12.2.2 > Problem12-118

12-118.

Given the infinite sum $a − \frac { a } { 2 } + \frac { a } { 4 } - \frac { a } { 8 }+\: ... = 24$, what is the value of $a$?

$S=\frac{a}{1-r}$

$r=-\frac{1}{2}$

$24=\frac{a}{1-(1/2)}$