[tex]Rab=\frac{R123.R4}{R123+R4}[/tex]
[tex]R123=R1+\frac{R2.R3}{R2+R3}[/tex]
[tex]U123=U4[/tex]
=> I123.R123=I4.R4
=> I123/I4=..
I123+I4=I
giải ra I123
Uab=I123.R123
b) dễ r
[tex]Rab=\frac{R123.R4}{R123+R4}[/tex]
[tex]R123=R1+\frac{R2.R3}{R2+R3}[/tex]
[tex]U123=U4[/tex]
=> I123.R123=I4.R4
=> I123/I4=..
I123+I4=I
giải ra I123
Uab=I123.R123
b) dễ r