RI R R 图(a)电路的回路方程 (R1+R2)1+4=1=0R,+R2 R 得R1上电流i1 R+r 1 us R2S=4+” R1+R2 Ri+R图(a)电路的回路方程： ( ) 3 S 1 2 1 2 3 S    = + + = i i R R i R i u 得R1上电流 i1 " 1 ' S 1 1 2 2 S 1 2 1 1 i i i R R R u R R i = + + − + + = S 1 2 2 1 0 " 1 S 1 2 1 0 ' 1 S S 1 i R R R i i u R R i i u i + − = = + = = = =