# The differential equation of the family $y=ae^x+bx\; e^x+cx^2\;e^x$ of curves, where $a,b,c$ are arbitrary constants, is :

$\begin {array} {1 1} (1)\;y'''+3y''+3y'+y=0 & \quad (2)\;y'''+3y''-3y'-y=0 \\ (3)\;y'''+3y''-3y'+y=0 & \quad (4)\;y'''-3y''+3y'-y=0 \end {array}$

$(4)\;y'''-3y''+3y'-y=0$