Exercise · ZW-REAL-INTEGRAL-BY-RESIDUES-002 · ★☆☆ Basic
Compute \(\int_{-\infty}^{\infty}\frac{dx}{x^{2}+4}\).
Choose one option.
Show answer
- D. \(\pi/2\)
Explanation
The upper pole is \(2i\) with residue \(1/(4i)\); \(2\pi i/(4i)=\pi/2\).
Review the concept: Real integral by residues
A method to compute \(\int_{-\infty}^{\infty} f(x)\,dx\) with \(f\) rational: close the real axis with a semicircle in the upper half-plane and apply the residue theorem.
\[\int_{-\infty}^{\infty} f(x)\,dx=2\pi i\sum_{\operatorname{Im}z_k>0}\operatorname{Res}(f,z_k)\]
More practice problems: real integral by residues
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- ZW-REAL-INTEGRAL-BY-RESIDUES-005 Compute ∫_-∞^∞(dx)/(x^2+2x+2).
- ZW-REAL-INTEGRAL-BY-RESIDUES-006 Compute ∫_-∞^∞(dx)/((x^2+1)^2).
- ZW-REAL-INTEGRAL-BY-RESIDUES-007 Compute ∫_-∞^∞(dx)/((x^2+1)(x^2+4)).
- ZW-REAL-INTEGRAL-BY-RESIDUES-008 Compute ∫_-∞^∞(dx)/(x^4+1).
- ZW-REAL-INTEGRAL-BY-RESIDUES-009 Let f=P/Q be rational with no real poles. Which condition guarantees that the integral over the sem…
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