例212 R1 R R BI G1+G2 G1 U G- Bl I R U=12R2 (R1+R3+r)R3 q R+R2+(1+B)R3+r• 例2.12 + - rI1 ßI2 I1 I2 R2 R1 R3 I + U + U2 G1 +G2 - G1 U I - G1 G1 +G3 U2 rI1 G3 - ßI2 = U-U2 = I1 R1 U = I2 R2 R R R r R R r R I U q + + + + + + = = 1 2 3 1 3 3 e (1 ) ( ) R 