y'''+y''+y'+y=x^2
thanks
The roots of the characteristic equation are $\displaystyle -1,\pm i$, so the general solution for the homogeneus is:
$\displaystyle y_h(x)=C_1e^{-x}+C_2\cos x+C_3\sin x$
A particular solution for the complete has the form :
$\displaystyle y_p(x)=Ax^2+Bx+C$
Try it.
Fernando Revilla