D 2.52 The circuit shown in Fig. P2.52 utilizes a 50- kΩ potentiometer to realize an adjustable-gain amplifier. Derive an expression for the gain as a function of the potentiometer setting x. Assume the op amp to be ideal. What is the range of gains obtained? Show how to add a fixed resistor so that the gain range can be 1 to 21 V/V. What should the resistor value be?