a, K mở
\(I_{A_1}=I=0,5A\\ R_{td}=\dfrac{U}{I}=\dfrac{6}{0,5}=12\\ R_{td}=R_1+R_5+\dfrac{R_2\left(R_3+R_1\right)}{R_2+R_3+R_1}=9+\dfrac{4\left(R_3+6\right)}{10+R_3}=12\\ 4\left(R_2+6\right)=3\left(10+R_3\right)\\ R_3=6\)
b, K đóng
\(R_{14}=2\Rightarrow R_{124}=6;R_{123}=3;R_{td}=9\\ \rightarrow I=\dfrac{U}{R_{td}}=\dfrac{6}{9}=\dfrac{2}{3}\)
\(I=I_{A_1}=\dfrac{2}{3}\\ I_{A_2}=I-I_4\\ U_{AB}=I.R_{AB}=\dfrac{2}{3}.3=2\\ \Rightarrow U_{124}=2\\ I_{14}=I_{124}=\dfrac{2}{6}=\dfrac{1}{3}\rightarrow U_{14}=\dfrac{1}{3}.2=\dfrac{2}{3}\\ I_4=\dfrac{U_{14}}{R_4}=\dfrac{\dfrac{2}{3}}{3}=\dfrac{2}{9}\rightarrow I_{A_2}=I-I_4=\dfrac{2}{3}-\dfrac{2}{9}=\dfrac{4}{9}\)
Tự vẽ lại hình ạ :<
