Residue Method for Integrating Complex Functions

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SUMMARY

The residue method for integrating complex functions is effectively demonstrated through the evaluation of the integral \(\int_{-\infty}^{\infty} \frac{dx}{x^2 + 1}\). The solution involves calculating the residue at the pole \(z = i\), leading to the result \(I = 2\pi i \cdot \left(-\frac{1}{2}i\right) = \pi\). The discussion confirms that the condition \(\Im(z) \ge 0\) is essential for the correct application of the residue theorem, validating the final answer of \(\pi\).

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Homework Statement


\int\limits^{\infty}_{-\infty}\frac{\mbox{d}x}{x^2+1}
and i must count this using residues

The Attempt at a Solution


I=2\pi i\left(\mbox{res}_i\frac{1}{z^2+1}\right)=2\pi i\left(\lim_{z\to i}(z-i)\frac{1}{(z-i)(z+i)}\right)=2\pi i\left(-\frac12i}\right)=\pi
correct?
 
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i don't know why edit doesn't work, but now i came to that these points must be for \Im(z)\ge0 and result will be \pi now, is this solution correct now?
there should have been \Im(z)\ge0
 
Yes, the answer \pi is correct. And it seems that your method is also good!
 

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