Chapter 9, Problem 15RE

Use any method to determine whether the series converge.

$\begin{array}{l}\text{(a)}{\displaystyle \underset{k=1}{\overset{\infty }{\sum }}\frac{1}{5^k}}\\ \text{(b)}{\displaystyle \underset{k=1}{\overset{\infty }{\sum }}\frac{1}{5^k+1}}\end{array}$