Representing a transmission line by the two-port network, in terms of $A B C D$ parameters, (a) express $V_{S}$, the sending-end voltage, in terms of $V_{R}$, the receiving-end voltage, and $I_{R}$, the receiving-end current, and (b) express $I_{S}$, the sending-end current, in terms of $V_{R}$ and $I_{R}$.(a) $V_{S}=$(b) $I_{S}=$