 Here the sink is to be analyzed by idealizing the op amp as a nullor.Using properties of the input nullator portion of the nullor, the input voltage across the op amp input terminals is zero.Consequently, the voltage across reference resistor "R"R is the applied voltage "v"IN, making the current in "R"R simply "v"IN/"R"R. Again using the nullator properties, the input current to the nullor is zero.