TeX source:
\begin{array}{rclcl} 5 x^2 - 80 &=& 0 & \vert & +80 \cr 5x^2 &=& 80 & \vert & :5 \cr x^2 &=& 16 & \vert & \pm \sqrt{} \cr x &=& \pm \sqrt{16} \cr\cr x_1 &=& 4 \cr x_2 &=& -4 \cr \cr \mathbb{L} &=& \{-4; 4\} \end{array}