In Exercises $1-3,$ begin by drawing a diagram that shows the relations among the variables.
If $w=x^{2}+y^{2}+z^{2}$ and $z=x^{2}+y^{2},$ find
a. $\left(\frac{\partial w}{\partial y}\right)_{z}$ b. $\left(\frac{\partial w}{\partial z}\right)_{x}$ c. $\left(\frac{\partial w}{\partial z}\right)_{y}$