How to prove that $\sin(x\sin x)$ is NOT uniformly continuous on positive reals

1.4k Views Asked by At

How to prove that $\sin(x \sin x)$ is not uniformly continuous on $\Bbb{R}^+$?

My attempt: I know that $\sin x$ is uniformly continuous on that interval when $\sin{x^2}$ is not.

Yes It is duplicate of one question. But the answer was not satisfactory. That's why I am posting it again.

Any help will be highly appreciated.

1

There are 1 best solutions below

0
On

Hint :

Take, $x_n=\{2n\pi \}_n$ and $y_n=\{2n\pi +\frac{\pi}{n}\}_n$. Then $|x_n-y_n|\to 0$ as $n \to \infty$.

But , $|f(x_n)-f(y_n)|\to \sin(2\pi^2)\not= 0$

Edit :

$$\lim_{n\to \infty}\left(2n\pi+\frac{\pi}{n}\right)\sin\left(2n\pi+\frac{\pi}{n}\right)=\lim_{n\to \infty}\left(2n\pi+\frac{\pi}{n}\right)\sin(\pi /n)=\lim_{n\to \infty}2n\pi \sin(\pi /n)=2\pi ^2$$ So , $$\lim_{n\to \infty}\sin \left[\left(2n\pi+\frac{\pi}{n}\right)\sin\left(2n\pi+\frac{\pi}{n}\right)\right]=\sin \left[\lim_{n\to \infty}\left(2n\pi+\frac{\pi}{n}\right)\sin\left(2n\pi+\frac{\pi}{n}\right)\right]=\sin(2.\pi^2)$$