\[x^{2} + y^{2} = 81\]
\[x^{2} + 0 = 81\]
\[x^{2} = 81\]
\[x = \pm 9.\]
\[Точки\ пересечения\ с\ Ox:\ \ \]
\[(9;0);\ \ ( - 9;0).\]
\[x^{2} + y^{2} = 81\]
\[0 + y^{2} = 81\]
\[y^{2} = 81\]
\[y = \pm 9\]
\[Точки\ пересечения\ с\ Oy:\ \ \]
\[(0;9);\ \ (0;\ - 9).\]
\[Ответ:(9;0);\ \ ( - 9;0),;\ (0;9);\ \ \]
\[(0;\ - 9)\text{.\ }\]