Lets analysis the following circuit.
This circuit consist of two nodes named as v1 & v2
Consider the input voltage is vin .
Lets say the current ‘i’ is passing through the node v2 .
Then the voltage at the node v2 is given by
Voltage at the node V1 is given by
Then the input voltage vin is given by
Substituting the value of V1 in equation 3 we get,