TeX source:
\begin{array}{rclll} \mathbb{D} &=& \mathbb{R} \cr\cr f'(x) &=& \dfrac{1}{8}x^2-\dfrac{1}{4}x-1 & \vert & \text{nullsetzen} \cr \cr 0 &=&\dfrac{1}{8}x^2-\dfrac{1}{4}x-1 \cr &...& \cr x_1 &=& -2 \cr x_2 &=& 4 \end{array}