Bourbaki

Exercise 30, § 1

Functions of a Real Variable, III, 123

a) If mm and nn are two integers such that 0<m<n0 < m < n show that

∫0+∞xm−11+xndx=πnsin⁡mπn. \int_0^{+\infty} \frac{x^{m-1}}{1 + x^n} dx = \frac{\pi}{n \sin \frac{m \pi}{n}}.
b) Show that for 0<a<10 < a < 1 the integral ∫0+∞xa−11+xdx\int_0^{+\infty} \frac{x^{a-1}}{1 + x} dx is uniformly convergent for aa varying in a compact interval, and deduce from a) that
∫0+∞xa−11+xdx=πsin⁡aπ. \int_0^{+\infty} \frac{x^{a-1}}{1 + x} dx = \frac{\pi}{\sin a \pi}.

Solution

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Transcribed from the printed volume. Not translated.