GATE EC 2016 Set 1 Q8 — Complex Analysis

Consider the sequence $x[n] = a^nu[n] + b^nu[n]$, where $u[n]$ denotes the unit-step sequence and $0<\mid a \mid < \mid b \mid<1$. The region of convergence (ROC) of the $Z$-transform of $x[n]$ is