I have found a proof using complex analysis techniques (contour integral, residue theorem, etc.) that shows ∫∞0dx1+xn=πnsinπn for n∈N+∖{1}
I wonder if it is possible by using only real analysis to demonstrate this "innocent" result?
Edit
A more general result showing that
$$\int\limits_{0}^{\infty} \frac{x^{a-1}}{1+x^{b}} \ \text{dx} = \frac{\pi}{b \sin(\pi{a}/b)}, \qquad 0 < a
can be found in another math.SE post
Answer
∫∞011+xn dx=∫∞0∫∞0e−(1+xn)t dt dx
=∫∞0∫∞0e−te−txn dx dt=1n∫∞0∫∞0e−te−u(ut)1n−11t du dt
=1n∫∞0t−1ne−t∫∞0u1n−1e−u du dt=1n∫∞0t−1ne−t Γ(1n) dt
=1n Γ(1−1n)Γ(1n)=πncsc(πn)
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