2.71 For the differential amplifier of Fig. P2.71, derive an expression for the output, vO, in terms of the differential input, vId = vI2 − vI1, and the potentiometer setting x. Note that the circuit acts as a difference amplifier whose output can be adjusted by the potentiometer setting. What is the change in output voltage when x is changed from 0 to 1? How may this range be increased?