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Contour integral of log x over x squared plus 2x plus 2

Question

Use contour integration to evaluate ∫0∞log⁡xx2+2x+2 dx.\int_0^{\infty}\frac{\log x}{x^2+2x+2}\,dx.

Short answer

πln⁡28≈0.2722\tfrac{\pi\ln2}{8}\approx0.2722. Integrate (log⁡z)2z2+2z+2\frac{(\log z)^2}{z^2+2z+2} around a keyhole contour (branch cut on the positive axis); the poles are z=−1±i=2e±3πi/4z=-1\pm i=\sqrt2e^{\pm3\pi i/4}. Matching imaginary parts with the residue sum isolates the log integral as πln⁡28\tfrac{\pi\ln 2}{8}, which numerical quadrature confirms.

Adapted from Joshi, Denson & Downes, Quant Job Interview Questions and Answers, Q6.26, p.191; question and answer rewritten by SelfMadeQuant.com.

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