TeX source:
\begin{array}{rclcl} -3x^2+363 &=& 0 & \vert & -363 \cr -3x^2 &=& -363 & \vert & :(-3) \cr x^2 &=& 121 & \vert & \pm \sqrt{} \cr\cr x_1 &=& 11 \cr x_2 &=& -11 \cr \cr \mathbb{L} &=& \{-11;11\} \end{array}