The solution of the ordinary differential equation $\dfrac{dy}{dx}+2y=0$ for the boundary condition, $y=5$ at $x=1$ is
1. $y=e^{-2x}$
2. $y=2e^{-2x}$
3. $y=10.95 e^{-2x}$
4. $y=36.95 e^{-2x}$