Đáp án:
${R_2} = 37,5\left( \Omega \right)$
${R_1} = 75\left( \Omega \right)$
Giải thích các bước giải:
cách 1:
$\begin{array}{l}
{R_1}//{R_2}\\
\Rightarrow {R_{td}} = \frac{{{R_1}{R_2}}}{{{R_1} + {R_2}}} = \frac{{2R_2^2}}{{3{R_2}}} = \frac{2}{3}{R_2}\\
{R_{td}} = \frac{U}{I} = \frac{{30}}{{1,2}} = 25 = \frac{2}{3}{R_2}\\
\Rightarrow {R_2} = 37,5\left( \Omega \right)\\
{R_1} = 2{R_2} = 75\left( \Omega \right)
\end{array}$
cách 2
$\begin{array}{l}
{R_1}//{R_2}\\
\Rightarrow {U_1} = {U_2} = U = 30\\
{I_1} = \frac{{{U_1}}}{{{R_1}}} = \frac{{30}}{{2{R_2}}};{I_2} = \frac{{{U_2}}}{{{R_2}}} = \frac{{30}}{{{R_2}}}\\
{I_1} + {I_2} = I\\
\Rightarrow \frac{{30}}{{2{R_2}}} + \frac{{30}}{{{R_2}}} = 1,2\\
\Rightarrow {R_2} = 37,5\left( \Omega \right)\\
{R_1} = 2{R_2} = 75\left( \Omega \right)
\end{array}$
