$$(D^2+D)y=x^2+2x+4$$
I found the solution as $$CF=C_{1}+e^{-x}C_{2}$$ and PI=$$\left(\frac{x^3}{3}\right)+4x$$
but the solution from my teacher is PI = $$\left(\frac{x^3}{3}\right)+4x+C3$$
Where This extra C3 is from, Is the solution right If I exclude the C3 ?