TeX Quellcode:

\begin{array}{rcl} f'_{zz}(x,y,z) &=& xy^2 e^{-3xy}\cdot (-1)\cdot z^{-1-1} \\\\ &=& -xy^2 e^{-3xy} z^{-2} \\\\ &=& -\dfrac{xy^2}{z^2} e^{-3xy}\end{array}