Does the improper integral +∞∫0xpsinxdx for p>0 converge?
Attempt. Limit of xpsinx as x tends to +∞ does not exist, in order to guarantee integral's divergence. So I worked on the definition. For p=1 we get the integral:
+∞∫0xsinxdx=lim (after integration by parts), which does not converge (the limit does not exist). This approach also works for p>1, but I had difficulties regarding the case p<1.
Thank you in advance.
Answer
If that integral converged, then as n\to \infty
\int_{2\pi n}^{2\pi n + \pi} x^p\sin x\, dx\to 0.
But this integral is greater than
(2\pi n)^p\int_{2\pi n}^{2\pi n + \pi} \sin x\, dx = (2\pi n)^p\cdot 2 \to \infty, contradiction.
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