a) Cấu trúc mạch: `R4nt[(R1ntR2)//R3]`
`R_{12}=R_{1}+R_{2}=1+2=3(Ω)`
`R_{123}=(R_{12}.R_{3})/(R_{12}+R_{3})=(3.2)/(3+2)=1,2(Ω)`
`R_{tđ}=R_{123}+R_{4}=1,2+0,8=2(Ω)`
`I_{AB}=U_{AB}/R_{tđ}=6/2=3(A)`
`I_{AB}=I_{4}=I_{123}=3(A)`
`U_{4}=I_{4}.R_{4}=3.0,8=2,4(V)`
`U_{123}=I_{123}.R_{123}=3.1,2=3,6(V)`
`U_{123}=U_{12}=U_{3}=3,6(V)`
`I_{3}=U_{3}R_{3}=(3,6)/2=1,8(A)`
`I_{12}=I_{123}-I_{3}=3-1,8=1,2(A)`
`I_{12}=I_{1}=I_{2}=1,2(A)`
`U_{1}=I_{1}.R_{1}=1,2.1=1,2(V)`
`U_{2}=I_{2}.R_{2}=1,2.2=2,4(V)`
b) `U_{AD}=U_{AC}+U_{CD}=U_{4}+U_{1}=2,4+1,2=3,6(V)`