kcl: i1+i2=i3...........(1)kvl: Us1=i1(R1+R4)+i3R3,将(1)代入,Us1=i1(R1+R3+R4)+i2R3,5=1530i1+510i2........(2)Us2=i2(R2+R5)+i3R3,将(1)代入,Us2=i2(R2+R3+R5)+i1R3,12=1840i2+510i1.......(3)(2)x3 -(1) 31=5010i2,i2=6.2mA,i1=1.2mA,i3=7.4mA。