# How do you find the sum of the infinite geometric series a1= 343, r=7, and a4= -1?

$S = 300.125$

#### Explanation:

For what I can see from the problem. The number sequence may probably be like as follows;

343 -49 7 -1

in this case, $r = - \frac{1}{7}$

and ${a}_{1} = 343$ and ${a}_{4} = - 1$

The formula for Sum of infinite geometric series with $0$<$r$<$1$ is

$S = {a}_{1} / \left(1 - r\right)$

$S = \frac{343}{1 - - \frac{1}{7}} = \frac{343}{\frac{8}{7}} = \frac{2401}{8} = 300.125$

God bless....I hope the explanation is useful.