# How do you find the sum of Sigma(-2/7)^n from n [0,oo)?

$- \frac{2}{7}$ is the common ratio of the Geometric Series in this problem.
Since $| - \frac{2}{7} | < 1$, the geometric series converges, and the sum of such a series -- where r is its common ratio -- is given by
${\sum}_{0}^{\infty} {\left(r\right)}^{n} = \frac{1}{1 - r}$