TeX source:
\begin{array}{rclcl} 9x^2+18x &=& 81 & \vert & :9 \cr x^2+2x &=& 9 & \vert & -9 \cr x^2+2x-9 &=& 0 \cr x_{1,2} &=& -1\pm\sqrt{1^2+9} \cr\cr x_1 &=& -1+\sqrt{10} \cr x_2 &=& -1-\sqrt{10} \cr \cr \mathbb{L} &=& \{-1+\sqrt{10};-1-\sqrt{10}\} \end{array}