\[\left\{ \begin{matrix} x + 2y = 0 \\ 2x - y = 5 \\ \end{matrix} \right.\ \]
\[\left\{ \begin{matrix} 2y = - x\ \ \ \ \ \\ y = 2x - 5 \\ \end{matrix} \right.\ \]
\[\left\{ \begin{matrix} y = - 0,5x\ \\ y = 2x - 5 \\ \end{matrix} \right.\ \]
\[Решение:(2; - 1).\]