Question:

The particular integral of \[ \frac{d^2y}{dx^2}+3\frac{dy}{dx}+2y=e^{-2x} \] is

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If \(F(a)=0\) for RHS \(e^{ax}\), use the repeated/root adjustment method and multiply by \(x\).
  • \(-xe^{-2x}\)
  • \(xe^{-2x}\)
  • \(-\frac{x}{2}e^{-2x}\)
  • \(\frac{x}{2}e^{-2x}\)
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The Correct Option is A

Solution and Explanation


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: \[ PI=-xe^{-2x} \] \[ \boxed{-xe^{-2x}} \]
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