GATE EC 2006 Set 1 Q30 — Circuit Analysis

A two-port network is represented by $\text{ABCD}$ parameters given by

$$\left[\begin{array}{c} \mathrm{V}_1 \\ \mathrm{I}_1 \end{array}\right]=\left[\begin{array}{ll} \mathrm{A} & \mathrm{B} \\ \mathrm{C} & \mathrm{D} \end{array}\right]\left[\begin{array}{c} \mathrm{V}_2 \\ -\mathrm{I}_2 \end{array}\right]$$

if port-$2$ is terminated by $\text{R}_\text{L},$ then input impedance seen at port-$1$ is given by