6)
R12 = 12*6/(12+6) Ом =4 Ом
R46 = 4*4/(4+4)=2 Ом
R456 = 2*2/(2+2)=1 Ом
Rэкв = 4 + 5 + 1 = 10 Ом
7)
I3=1A
U3=I3*R3=1*12=12 B
U(BC)=U3=12 B
U2=U3= 12 B
I2 = U2/R2 = 12/6 = 2 A
I1=I2+I3=1+2=3 A
U1= I1*R1 = 3*4 = 12 B
I4=I1= 3A
U4 = I4*R4 = 3*2 = 6 B
U(CD)=U4= 6 B
U(AD)=U1+U2+U4=U1+U3+U4= 12+12+6 = 30 B
8)
R23=2*3/(2+3)=1,2 Ом
R123 = 1,2+1,8= 3 Ом
I =I1 = U/R123=30/3 = 10 А
U1 = I1*R1 = 10*1,8 = 18 В
U2=U3=U-U1=30-18=12 B
I2 = U2/R2= 12/2 = 6A
I3 = U3/R3 = 12/3 = 4 A или I3 = I - I2 = 10 - 6 = 4 A