\[x² - 10x + 18 = 0\]
\[\left\{ \begin{matrix} x_{1} + x_{2} = 10 \\ x_{1} \cdot x_{2} = 18\ \ \\ \end{matrix} \right.\ \]
\[\Longrightarrow x_{1} = 5 + \sqrt{7};\ \ x_{2} = 5 - \sqrt{7}.\]