TeX Quellcode:

\begin{array}{rcl}f'_y(x,y) &=& \dfrac{0\cdot\left(x+9y\right)-6\ln(x)\cdot 9}{\left(x+9y\right)^2} \\\\&=& -\dfrac{54\ln(x)}{(x+9y)^2}\end{array}