Derivative Of Multivariable Function

#Math

$\displaystyle dz(x,y)=\frac{ \partial z }{ \partial x }\mathrm{d}x+\frac{ \partial z }{ \partial y }\mathrm{d}y=\nabla z\cdot \mathrm{d}l$

• $\displaystyle \nabla z$ is the gradient of $\displaystyle z$