Using residues, evaluate the integral -8 x² (x² + 1)(x² +9) dx

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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**Problem Statement:**

Using residues, evaluate the integral

\[
\int_{-\infty}^{\infty} \frac{x^2}{(x^2 + 1)(x^2 + 9)} \, dx
\]

**Explanation:**

- This integral is to be evaluated over the entire real line.
- The function \( \frac{x^2}{(x^2 + 1)(x^2 + 9)} \) is a rational function that needs to be analyzed using complex analysis, specifically the method of residues.
- The poles of the integrand, which are the roots of the denominators \( x^2 + 1 = 0 \) and \( x^2 + 9 = 0 \), are critical in applying residue calculus. These poles are \( x = i, -i, 3i, -3i \) in the complex plane.
- The goal is to find the residues at these poles that lie in the upper half of the complex plane and use them to evaluate the original integral.
Transcribed Image Text:**Problem Statement:** Using residues, evaluate the integral \[ \int_{-\infty}^{\infty} \frac{x^2}{(x^2 + 1)(x^2 + 9)} \, dx \] **Explanation:** - This integral is to be evaluated over the entire real line. - The function \( \frac{x^2}{(x^2 + 1)(x^2 + 9)} \) is a rational function that needs to be analyzed using complex analysis, specifically the method of residues. - The poles of the integrand, which are the roots of the denominators \( x^2 + 1 = 0 \) and \( x^2 + 9 = 0 \), are critical in applying residue calculus. These poles are \( x = i, -i, 3i, -3i \) in the complex plane. - The goal is to find the residues at these poles that lie in the upper half of the complex plane and use them to evaluate the original integral.
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