Is Squeeze Theorem Relevant Here?

Calculus Level 1

lim x 0 sin ( 1 x ) = ? \large \lim_{x\to0^-} \sin \left( \dfrac1x\right) = \, ?

Submit your answer as 1337 if you think the limit fails to exist.


The answer is 1337.

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2 solutions

Sravanth C.
Feb 24, 2016

The function f ( x ) = sin ( 1 / x ) f(x)=\sin(1/x) oscillates rapidly from 1 -1 to + 1 +1 as x 0 x\rightarrow 0 , and the oscillation is too much for the function to have a limit(see the image).

Graph of the function y=sin(1/x) Graph of the function y=sin(1/x)

This type of discontinuity is sometimes referred to as oscillating discontinuity , according to which a function seems to be approaching two different values, and in this case it seems to be approaching 1 1 or 1 -1 . Thus the limit doesn't exsist.

I don't see why "it is hard to tell whether the function is approaching 1 or -1". Isn't it clear that the limit is neither of them?

More accurately, I would say that "We can find subsequences whose limits are different".

Calvin Lin Staff - 5 years, 3 months ago

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Oh alright, I've edited it. If you think it can further be improved, please reply sir.

Sravanth C. - 5 years, 3 months ago

Let x k = 1 2 π k x_k = \frac {-1}{2\pi \cdot k} when k k \rightarrow \infty ( x 0 x \to 0^{-} ) and k N k \in \mathbb{N} , then the limit above is 0.

Now, let x k = 1 π 2 + 2 π k x_k = \frac {-1}{ \frac {\pi}{2} + 2\pi \cdot k} when k k \rightarrow \infty and k N k \in \mathbb{N} , then the limit above is -1.

Therefore, the limit above doesn't exist due to definition of limit

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