Đáp án:
\(\left( {x;y} \right) = \left( {\dfrac{{ - 1}}{5};\dfrac{8}{5}} \right)\)
Giải thích các bước giải:
$\begin{array}{l}
\left\{ \begin{array}{l}
3x + y = 1\\
- x - 2y = - 3
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
y = 1 - 3x\\
- x - 2\left( {1 - 3x} \right) = - 3
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
y = 1 - 3x\\
- x - 2 + 6x = - 3
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
y = 1 - 3x\\
5x = - 1
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
y = 1 - 3.\dfrac{{ - 1}}{5}\\
x = \dfrac{{ - 1}}{5}
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
y = \dfrac{8}{5}\\
x = \dfrac{{ - 1}}{5}
\end{array} \right.\\
Vay\; \left( {x;y} \right) = \left( {\dfrac{{ - 1}}{5};\dfrac{8}{5}} \right).
\end{array}$
