(5)
I=I1+I2, I2=4mA
I1R1+I3R3-I2R2=0
6*3+I3*2-4*1=0
I3=-7mA
I1=I3+I4
I4=13mA
I2+I3+I5=0
I5=-I2-I3=4+7=11mA
(6) 2I1+2I3=14-4=10
I1=5-I3=3A
I2=I1-I3=1A
2I1+I2R2=14
R2=14-6=8Ω
(7)
设20Ω支路电流I1,5Ω支路电流I2
I=I1+I2 ①
并联电路两端电压相等:14-20I1=9-5I2=6I ②
由① ②可得 I=1 A, I1=0.4 A , I2=0.6A
(8)Rab=4Ω