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GATE 2024 BM – Question 44

Engineering Mathematics · Complex Variables · 2 marks · Multiple choice

Using residues, evaluate $\int_{-\infty}^{\infty}\frac{dx}{1+x^4}$.

  1. $\pi/\sqrt2$
  2. $\pi/(2\sqrt2)$
  3. $\pi/4$
  4. $\pi/2$

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Correct answer: (A) $\pi/\sqrt2$

Explanation

Close the contour in the upper half-plane. The enclosed simple poles are eⁱπ/⁴ and e³ⁱπ/⁴, each with residue 1/(4z³). Their sum is −i/(2√2). The large semicircle contributes zero because the integrand decays as 1/z⁴. Hence the real integral is 2πi×[−i/(2√2)]=π/√2, A.

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