\small u_0 = \dfrac {1 + s \, \left[ \, C_1 \left( R_1 + R_2 \right) + C_2 \, R_2 \, \right] + s^2 \, C_1 \, C_2 \, R_1 \, R_2 + s \, C_2 \, R_0 \, \left[ \, 1 + s \, C_1 \left( R_1 + R_2 \right) \, \right]} {s^2 \, C_1 \, C_2 \, R_1 \, R_2} \ u_1