[tex]I=xze^{-y^2-z^2}[/tex]
[tex]\mathrm dI=\dfrac{\partial I}{\partial x}\,\mathrm dx+\dfrac{\partial I}{\partial y}\,\mathrm dy+\dfrac{\partial I}{\partial z}\,\mathrm dz[/tex]
[tex]\mathrm dI=ze^{-y^2-z^2}\,\mathrm dx-2yxze^{-y^2-z^2}\,\mathrm dy+\left(x-2xz^2\right)e^{-y^2-z^2}\,\mathrm dz[/tex]
