TeX source:
\begin{array}{rcl}f'_{xy}(x,y,z) &=& 3\cdot\dfrac{1}{2}x^1y^{\frac{1}{2}-1}z^3+\dfrac{4}{3}\cdot 2x^{-\frac{2}{3}}y^{2-1}\\\\&=& \dfrac{3}{2}x^1y^{-\frac{1}{2}}z^3+\dfrac{8}{3}x^{-\frac{2}{3}}y\end{array}