# Prove that the $\lim_{x \rightarrow 0}\frac1x$ does not exist

we have been doing epsilon and delta limit proofs in my first year calculus class and I can't seem to wrap my around this stuff. We have not done an example in class of disproving a limit, and this was given as a practice question for my exam so I really need some help, Thank You!

Prove that the $\lim_{x \rightarrow 0}\frac1x$ does not exist

• $$\lim_{x\to0^+}\frac1x=+\infty, \lim_{x\to0^-}\frac1x=-\infty$$ – lab bhattacharjee Dec 10 '13 at 10:56
• Yeah I unnderstand that, but I need to prove it using the definition of a limit (epsilons and deltas) Thanks! – Alex Chavez Dec 10 '13 at 10:57

## 1 Answer

Show that no number $\alpha \in \mathbb R$ is a limit of $\frac 1x$ for $x \to 0$. That is show that $$\exists \epsilon > 0 \; \forall \delta > 0 \; \exists x:\; x \in (-\delta, \delta) \land\left|\frac 1x - \alpha\right| > \epsilon$$ Let $\epsilon = 1$ and given $\delta$, set $x = \min\{\frac\delta 2, \frac 1{|\alpha| + 2}\}$.