\[\left\{ \begin{matrix} y - x = 0\ \ \ \\ 3x + y = 8 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} y = x\ \ \ \ \ \ \ \ \ \ \\ 3x + x = 8 \\ \end{matrix} \right.\ \text{\ \ \ \ \ }\]
\[\left\{ \begin{matrix} y = x\ \ \\ 4x = 8 \\ \end{matrix} \right.\ \text{\ \ \ \ \ }\]
\[\left\{ \begin{matrix} x = 2 \\ y = 2 \\ \end{matrix} \right.\ \]
\[Проверка:\ \]
\[\left\{ \begin{matrix} 2 - 2 = 0\ \ \ \ \ \ \\ 3 \cdot 2 + 2 = 8 \\ \end{matrix} \right.\ \text{\ \ \ \ }\]
\[\left\{ \begin{matrix} 0 = 0 \\ 8 = 8 \\ \end{matrix} \right.\ \Longrightarrow верно.\]
\[Ответ:(2;2).\]