[UPSC CSE 2003] Semiconductors/Solar cell (Q256, 20M)

In the following circuit, Show that the stability factor, S, is given by

S = \frac{1 + \beta}{1 + \frac{\beta R_e}{R_e + R_b}} Where R_b = \frac{R_1 R_2}{R_1 + R_2}