\[\left\{ \begin{matrix}
x^{2} + y^{2} = 16 \\
y + x = 0\ \ \ \ \ \ \ \\
\end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\left\{ \begin{matrix}
x^{2} + y^{2} = 4^{2} \\
y = - x\ \ \ \ \ \ \ \ \ \ \ \\
\end{matrix} \right.\ \]

\[Ответ:(2,8; - 2,8);\ \ ( - 2,8;2,8).\]