R1 NT(R2//R3) goi dien tro \(R3=x\left(\Omega\right)\)
\(\Rightarrow I1=\dfrac{9}{R1+\dfrac{R2x}{R2+x}}=\dfrac{9}{7+\dfrac{2,5x}{2,5+x}}=\dfrac{5}{4}I2\)
\(\Rightarrow\dfrac{9}{7+\dfrac{2,5x}{2,5+x}}=\dfrac{5}{4}.\left(\dfrac{U2}{2,5}\right)=0,5U2=0,5\left(9-U1\right)=0,5\left\{9-I1.R1\right\}=0,5\left\{9-\dfrac{63}{7+\dfrac{2,5x}{2,5+x}}\right\}\Rightarrow x=R3=10\Omega\)