最简单的串并联电路，求解..

R2与R3并联等效电阻
R23=R2*R3/(r2+R3)=4*6/(4+6)=2.4欧
电路总电阻R=R1+R23=2+2.4=4.4欧
I1=U/R=12/4.4=2.73A
U2=U3=U-U1=U-I1*R1=12-2*2.73=6.54V
I2=U2/R2=6.54/4=1.6A
I3=I1-I2=2.73-1.6=1.13A

R=R2R3/(R2+R3)+R1=4*6/10+2=4.8
I=U/R=12/4.8=2.5A
由于R1在干路中 故I1=2.5A
R2和R3并联，由并联电路分流与电阻成反比
而电阻之比为R2/R3=2/3
故分流比为3/2 因此
I2=(3/5)*I=1.5A I3=2.5-1.5=1A

I(R1)=U/R
=12/(R1+R并)=12/[R1+1/(1/R2+1/R3)]
=12/[2+1/(1/4+1/6)]
=30/11

I(R2)=U2/R2=I(R1)*R并/R2=18/11
I(R3)=I(R1)-I(R2)=12/11

并联:1/R总=1/R1+1/R2=1/4+1/6=5/12欧姆
R总=12/5+2=4.4欧姆
串联： I1=U/R=12/4.4=30/11A=2.7A
并联中: I2+I3=I1=30/11A
I2:I3=R3:R2=3:2
I2=30/11/5*3=18/11A=1.6A
I3=30/11-18/11=12/11A=1.1A

总电阻为4.4欧
总电流2.727A=1中电流
R2\R3分流比3：2
所以2中1.636
3中1.0909

R2与R3并联的等效电阻
R23=R2*R3/(r2+R3)=4*6/(4+6)=2.4欧
所以总电阻R=R1+R23=2+2.4=4.4欧
I1=U/R=12/4.4=30/11A
I2/I3=R3/R2=3/2
I2+I3=30/11A