## Calculus (3rd Edition)

$$w_x= \frac{1}{y+z} ,\quad w_y= -x(y+z)^{-2},\quad w_z=-x(y+z)^{-2}.$$
Recall that $(x^n)'=nx^{n-1}$ Since $w=\frac{x}{y+z}=x(y+z)^{-1}$, we have $$w_x= \frac{1}{y+z} ,\quad w_y= -x(y+z)^{-2},\quad w_z=-x(y+z)^{-2}.$$