TeX source:
\begin{array}{rclcl}4x^2-1 &=& 0 &\vert & +1 \\4x^2 &=& 1 &\vert & :4 \\x^2 &=& \dfrac{1}{4} &\vert & \pm\sqrt{} \\x &=& \pm\dfrac{1}{2} \\\\\mathbb{L} &=& \left\{-2;-\dfrac{1}{2};\dfrac{1}{2}\right\}\end{array}