Step 1: Given:
\[
(D^2+3D+2)y=e^{-2x}
\]
Step 2: Factor operator:
\[
D^2+3D+2=(D+1)(D+2)
\]
Step 3: For RHS \(e^{-2x}\), put \(D=-2\):
\[
F(-2)=(-2)^2+3(-2)+2
\]
\[
=4-6+2=0
\]
Step 4: Since \(F(-2)=0\), ordinary substitution fails. Because \((D+2)\) is a factor, multiply by \(x\).
Step 5: The particular integral becomes:
\[
PI=-xe^{-2x}
\]
\[
\boxed{-xe^{-2x}}
\]