1. The problem statement, all variables and given/known data Find the appropiate particular solution form for y''' - y'' - 12y' = x - 2x*e^-(3x) DO NOT SOLVE FOR THE COEFFICIENTS 2. Relevant equations Just guessing proper solution forms for nonhomogeneous second order D.Es with undetermined coefficients. 3. The attempt at a solution Ok, as far as I know the solution in my mind was... Ax + B + (Cx^2 + Dx) e ^(-3x) The homogeneous solution was yc = c1 + c2e^(4x) + c3e^(-3x) BUT the solution is Ax + Bx^2 + (Cx + Dx^2)e^(-3x) I don;t know why the B has x^2, and I don't know why D and C are switched around. I've been going at this for a good hour.