TeX Quellcode:

\begin{array}{rclcl} A'(b) &=& 18-2b \cr\cr 0 &=& 18-2b &\vert& +2b \cr 2b &=& 18 &\vert& \cdot \dfrac{1}{2} \cr b &=& 9 \cr \cr a &=& 18-9 = 9 \end{array}