a)
b) Ta có: \(R_{tđ_1}=\dfrac{U}{I}=\dfrac{6}{0,4}=15\Omega\)
\(\Leftrightarrow R_1+R_2=15\left(1\right)\)
Ta có: \(R_{tđ_2}=\dfrac{U}{I'}=\dfrac{6}{1,8}=\dfrac{10}{3}\Omega\)
\(\Leftrightarrow\dfrac{R_1R_2}{R_1+R_2}=\dfrac{10}{3}\Leftrightarrow R_1R_2=50\left(2\right)\)
Từ (1)(2) ta có: \(\left\{{}\begin{matrix}R_1+R_2=15\\R_1R_2=50\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}R_1=15-R_2\\R_2^2-15R_2+50=0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}R_1=15-R_2\\\left(R_2-5\right)\left(R_2-10\right)=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}R_1=15-R_2\\\left[{}\begin{matrix}R_2=5\\R_2=10\end{matrix}\right.\end{matrix}\right.\)
* Với R2 = 5 thì R1 = 10
* Với R2 = 10 thì R1 = 5