TeX Quellcode:

\begin{array}{rcl}f'_{yx}(x,y) &=& -\cos\left(-\dfrac{1}{4}x+y\right)\cdot \left(-\dfrac{1}{4}\right)\\&=& \dfrac{1}{4}\cos\left(-\dfrac{1}{4}x+y\right)\end{array}