-E2=I2R2+I3R3

I1=0A,I2=-2A,I3=-2A

22．用支路法求出I1=I3=-2A，I2=0，Va=2V 23.I3=3A 24.I=1/3A

25.I3=I1+I5 E1=I1R1+I4R4-I5R5

I4=I1+I2 -E2=-I2R2-I6R6-I4R4

I6=I3+I2 E3=I3R3+I5R5+I6R6 26.(1)串联 R=R1+R2+R3=170Ω (2)并联 R=R1//R2//R3=12.5Ω （3）混联（a）,先串后并 R=（R3+R2）//R1=41.1Ω R=(R1+R3)//R2=35.3Ω R=（R1+R2）//R3=17.64Ω 混联（b）,先并后串 R=(R1//R2)+R3=53.3Ω R=(R3//R2)+R1=114.3Ω R=(R1//R3)+R2=66.7Ω