I am trying to compute the following limit,
limk→∞∫10|sin(kx)x|dx
After some numerical calculations, it loos like the limit is ∞. To prove it, I tried to use Riemann sums but such approach is not working.
Any hints on how one should prove this ?
Thanks in advance.
Answer
Changing variables (y=kx) this is
limk→∞∫k0|siny|ydy=∫∞0|siny|ydy.
This improper integral is well-known to diverge. For instance
∫nπ(n−1)π|siny|ydy≥1nπ∫π0sinydy=2nπ.
Adding these up, and considering the behaviour of the harmonic
series shows the integral diverges.
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