Write the closed-loop transfer function- what is the

Question

Consider the noninverting op-amp circuit in Figure P12.18. The input resistance of the op-amp is R_i = ∞ and the output resistance is R_o = 0, but the opamp has a finite gain A.

(a) Write the closed-loop transfer function in the form

(b) What is the expression for β?

(c) If A = 105 and A_{v f} = 20, what is the required β and R₂/R₁?

(d) If A decreases by 10 percent, what is the percent change in A_{v f} ?