4. (10%) Derive the transfer function \( V{\mathrm{out}} / V{\mathrm{in}} \) for the circuit in Fig. 4 with \( A_0 = \infty \).
4. (10%) Derive the transfer function \( V{\mathrm{out}} / V{\mathrm{in}} \) for the circuit in Fig. 4 with \( A_0 = \infty \).