TeX source:
\begin{array}{rclcl} z^2-56z+768 &=& 0 &\vert& \text{p-q-Formel} \cr z_{1,2} &=& 28 \pm \sqrt{\left(-28\right)^2-768} \cr &=& 28 \pm \sqrt{16} \cr\cr z_1 &=& 28+4 = 32 \cr z_2 &=& 28-4 = 24 \end{array}