TeX source:
\begin{array}{rcl} f'_x(x,y,z) &=& 300\cdot \dfrac{1}{2}\left(x+yz\right)^{\frac{1}{2}-1} \cdot 1\cr \cr &=& 150\left(x+yz\right)^{-\frac{1}{2}} \cr \cr&=& \dfrac{150}{\sqrt{x+yz}} \end{array}