Right choice is (c) VO = Ad × Vd + AC × VC
The best explanation: The differential gain of a differential amplifier with active load is defined as the gain obtained at the output signal with respect to the difference in the input signals applied. To calculate the output voltage of a differential amplifier with active load we use Ad × Vd + AC × VC. Where, Ad is the differential gain and AC and VC represent the common mode gain.