Analysis - Radius, Interval of Convergence, Elementary function which is the sum of the series

Determine the radius of convergence of every series below and find an elementary function which is the sum of the series in the corresponding interval of convergence. (a) \sum_{n=1}^{infinity} x^n /n; (b) \sum_{n=1}^{infinity} x^n /(n(n + 1)).