\[\frac{\partial}{\partial v}f(x(u,v),y(u,v),z(u,v))=\frac{\partial f}{\partial x%
}\frac{\partial x}{\partial v}+\frac{\partial f}{\partial y}\frac{\partial y}{%
\partial v}+\frac{\partial f}{\partial z}\frac{\partial z}{\partial v}.\]