giải giúp mình câu 4 với ạ

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a) `R_1` nối tiếp `R_2`: `R_{12}=R_1+R_2=9+16=25 (\Omega)`

`R_{12}` song song `R_3`: `R_{tđ}=R_{123}=\frac{R_{12}R_3}{R_12+R_3}=\frac{25.24}{25+24}=\frac{600}{49}(\Omega)`

b) `I=I_{123}=\frac{\xi}{r+R_{tđ}}=\frac{12}{0,6+\frac{600}{49}}=\frac{980}{1049}(A)`

`\Rightarrow U_{123}=U_{12}=U_3=IR_{tđ}=\frac{980}{1049}.\frac{600}{49}=\frac{12000}{1049}(V)`

`\Rightarrow I_3=\frac{U_3}{R_3}=\frac{\frac{12000}{1049}}{24}=\frac{500}{1049}\approx 0,48(A)`

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