How to show that:
$$\lim_{x\rightarrow 0} \frac{1}{x}\int_0^x |\sin(1/y)| \mathrm{d} y \not=0$$
It seems like a easy example of illustrating 0 is not in the Lebesgue set of $g(x)$ where $g(x)=\sin(1/x)$ if $x\neq 0$ and $g(0)=0$. But I fail to see why the above integral is true.
I tried looking at the intervals such that $\sin(1/y)$ is greater or equal to some constant (for example, $\left[\frac{1}{k\pi+\pi/6}, \frac{1}{k\pi+5\pi/6}\right]$ such that $\sin(1/y)\geq \frac{1}{2}$), however, $$\sum_{k \text{ large}} \left(\frac{1}{k\pi+\pi/6}-\frac{1}{k\pi+5\pi/6}\right)$$ converges, which is not strong enough to prove the claim. Any thoughts? Thanks in advance.
Let $y= 1/t$. We then get that $$I(x) = \dfrac1x \int_0^x \left \vert \sin(1/y) \right \vert dy = \dfrac1x \int_{\infty}^{1/x} \left \vert \sin(t) \right \vert \dfrac{-dt}{t^2} = \dfrac1x \int_{1/x}^{\infty} \dfrac{\left \vert \sin(t) \right \vert}{t^2} dt$$ Let $x=\dfrac1{n \pi}$. Hence, \begin{align} I_n & = n \pi \int_{n \pi}^{\infty} \dfrac{\vert \sin(t) \vert}{t^2} dt\\ & =n \pi \left(\sum_{k=n}^{\infty} \int_{k \pi}^{(k+1) \pi} \dfrac{\vert \sin(t) \vert}{t^2} dt \right)\\ & \geq n \pi \left(\sum_{k=n}^{\infty} \int_{k \pi}^{(k+1) \pi} \dfrac{\vert \sin(t) \vert}{(k+1)^2 \pi^2} dt \right)\\ & = n \pi \sum_{k=n}^{\infty} \left(\dfrac{1}{(k+1)^2 \pi^2}\displaystyle \int_{k \pi}^{(k+1) \pi} \vert \sin(t) \vert dt \right)\\ & = n \pi \sum_{k=n}^{\infty} \dfrac2{(k+1)^2 \pi^2}\\ & = \dfrac{2n}{\pi} \sum_{k=n}^{\infty} \dfrac1{(k+1)^2}\\ & > \dfrac{2n}{\pi} \int_{n+1}^{\infty} \dfrac{dt}{t^2}\\ & = \dfrac{2n}{\pi(n+1)} \end{align} Hence, we if let $x = \dfrac1{n \pi}$, then we get that $$I\left( \dfrac1{n \pi} \right) = I_n \geq \dfrac{2n}{\pi(n+1)}$$ Hence, $$\lim_{n \to \infty} I\left( \dfrac1{n \pi} \right) \geq \dfrac{2}{\pi}$$