Решите систему уравнений 4x-y=9; 3x+7y=-1.

\[\left\{ \begin{matrix} 4x - y = 9\ \ \ | \cdot 7 \\ 3x + 7y = - 1\ \ \ \ \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]

\[\left\{ \begin{matrix} 28x - 7y = 63\ \ \ \ (1) \\ 3x + 7y = - 1\ \ \ \ \ (2) \\ \end{matrix} \right.\ \]

\[(1) + (2) \Longrightarrow 31x = 62\]

\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = 2.\]

\[\left\{ \begin{matrix} x = 2\ \ \ \ \ \ \ \ \ \ \\ y = 4x - 9 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\left\{ \begin{matrix} x = 2\ \ \ \ \ \ \ \ \ \ \ \ \ \\ y = 4 \cdot 2 - 9 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\]

\[\left\{ \begin{matrix} x = 2\ \ \ \ \\ y = - 1 \\ \end{matrix} \right.\ \]

\[Ответ:(2;\ - 1).\]