Bài 3:
$R_{1}=R_{2}=2$ ôm
$R_{3}=1$ ôm
$R_{4}=3$ ôm
$R_{5}=4$ ôm
$U_{MN}=10,4V$
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a, Sđmđ: $\{[(R_{1}//R_{2})ntR_{3}]//R_{4}\}ntR_{5}$
$R_{12}=\dfrac{R_{1}.R_{2}}{R_{1}+R_{2}}=\dfrac{2.2}{2+2}=1$ ôm
$R_{123}=R_{12}+R_{3}=1+1=2$ ôm
$R_{1234}=\dfrac{R_{123}.R_{4}}{R_{123}+R_{4}}=\dfrac{2.3}{2+3}=1,2$ ôm
$R_{MN}=R_{1234}+R_{5}=1,2+4=5,2$ ôm
$⇒I_{5}=I=\dfrac{U_{MN}}{R_{MN}}=\dfrac{10,4}{5,2}=2A$
$⇒U_{5}=I_{5}.R_{5}=2.4=8V$
$⇒U_{4}=U_{3}+U_{1}=U_{MN}-U_{5}=10,4-8=2,4V$
$⇒I_{3}=\dfrac{U_{4}}{R_{123}}=\dfrac{2,4}{2}=1,2A$
$⇒U_{3}=I_{3}.R_{3}=1,2.1=1,2V$
$⇒U_{AN}=U_{3}+U_{5}=8+1,2=9,2V$
