$2\mathrm{.}2$

$8.e^{x}y\frac{dy}{dx}=e^{-y}{e}^{-2x-y}$

$\frac{dy}{dx}=g(x)h(y),{\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}u*dv=uv-{\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}$vdu