TeX source:
\begin{array}{rclcl} 2x^2+8 &=& 0 & \vert & -8 \cr 2x^2 &=& -8 & \vert & :2 \cr x^2 &=& -4 &\vert& \pm\sqrt{} \cr x &=& \pm\sqrt{-4} \end{array}