Решите систему уравнений: x-y=9; 2x+y=3.

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

\[3x = 12\]

\[x = 4.\]

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

\[\left\{ \begin{matrix} x = 4\ \ \ \\ y = - 5 \\ \end{matrix} \right.\ \]

\[Ответ:(4; - 5).\]