TeX Quellcode:

\begin{array}{rcl}\dfrac{f}{2} &=& \sqrt{a^2-p^2} \cr \dfrac{f}{2} &=& \sqrt{(2 \,cm)^2-(1 \, cm)^2} \cr \dfrac{f}{2} &=& \sqrt{3} \, cm \cr f&=& 2\sqrt{3} \, cm \end{array}