\[\sqrt{11}\ \ и\ - \sqrt{11}\]
\[x_{1} + x_{2} = \sqrt{11} - \sqrt{11} = 0;\]
\[x_{1} \cdot x_{2} = \sqrt{11} \cdot \left( - \sqrt{11} \right) = - 11.\]
\[Уравнение:\]
\[x^{2} + 0 \cdot x - 11 = 0\]
\[\Longrightarrow x^{2} - 11 = 0.\]