Решите систему уравнений:3x+7y=-5; 5x+4y=7.

\[\left\{ \begin{matrix}
3x + 7y = - 5\ \ \ | \cdot 5\ \ \ \ \ \\
5x + 4y = 7\ \ \ | \cdot ( - 3) \\
\end{matrix} \right.\ \text{\ \ \ \ \ }\]

\[\left\{ \begin{matrix}
15x + 35y = - 25\ \ \ \ \ \ (1) \\
- 15x - 12y = - 21\ \ (2) \\
\end{matrix} \right.\ \]

\[23y = - 46\ \ \]

\[y = - 2\]

\[\left\{ \begin{matrix}
y = - 2\ \ \ \ \ \ \ \ \ \ \ \ \\
3x + 7y = - 5 \\
\end{matrix}\ \right.\ \text{\ \ \ \ }\]

\[\left\{ \begin{matrix}
y = - 2\ \ \ \ \ \ \ \ \ \ \ \ \ \\
3x = - 5 - 7y \\
\end{matrix} \right.\ \text{\ \ \ \ \ }\]

\[\left\{ \begin{matrix}
y = - 2\ \ \ \ \ \ \ \ \ \ \ \ \\
x = - \frac{5}{3} - \frac{7}{3}y \\
\end{matrix} \right.\ \]

\[\left\{ \begin{matrix}
y = - 2\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\
x = - \frac{5}{3} - \frac{7}{3} \cdot ( - 2) \\
\end{matrix} \right.\ \text{\ \ \ \ \ }\]

\[\ \left\{ \begin{matrix}
y = - 2\ \ \ \ \ \ \ \ \ \ \ \\
x = - \frac{5}{3} + \frac{14}{3} \\
\end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\]

\[\left\{ \begin{matrix}
y = - 2\ \ \ \ \ \ \\
x = \frac{9}{3} = 3 \\
\end{matrix} \right.\ \]

\[Ответ:(3;\ - 2).\]