Bourbaki

Exercise 3, § 2

Functions of a Real Variable, VII, 328

Let ss be a fixed real number; show that when tt tends to +∞+\infty or to −∞-\infty one has

∣Γ(s+it)∣∼2π ∣t∣s−1/2 e−(π/2)∣t∣ |\Gamma(s + it)| \sim \sqrt{2\pi} \ |t|^{s-1/2} \ e^{-(\pi/2)|t|}
and
Γ′(s+it)Γ(s+it)∼log⁡∣t∣. \frac{\Gamma'(s + it)}{\Gamma(s + it)} \sim \log |t| .

Solution

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Transcribed from the printed volume. Not translated.