Chapter 5.2, Problem 93E

For $a_n$as follows, write the sum as a geometric series of the form ${\displaystyle \underset{n=1}{\overset{\infty }{\sum }}a{r}^n}$. State whether the series converges and if it does, find the value of ${\displaystyle \sum a_n}$.

93. $a_1=-1\text{and}{a}_n/a_{n+1}=-5\text{for}n\ge 1$