# $\frac{-1}{0}$ is infinity or -infinity? [duplicate]

Possible Duplicate:
Division by $0$

I was solving a question for my brother today when i got this doubt, i

I arrived at the answer as $\frac{-1}{0}$

Will the answer be infinity since any finite number divided by zero is infinity or should i write it as - $\frac{-1}{0}$ = - infinity ?

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## marked as duplicate by Rudy the Reindeer, Listing, David Mitra, Asaf Karagila, Zhen LinDec 31 '11 at 15:47

It is neither -- division by zero is undefined (it is not "infinity" because infinity is a concept, not a number). So you don't have an answer, but you possibly have an argument that there is no answer to whatever the original question is. – Henning Makholm Dec 31 '11 at 15:27
An argument that involves division by $0$ is never correct, though the intuitive idea behind it can often be turned into a correct argument. You would need to supply the actual problem to get more detail. – André Nicolas Dec 31 '11 at 15:28
– sdcvvc Dec 31 '11 at 15:28
I think he means limits of the form $\frac{-1}{0}$. – Listing Dec 31 '11 at 15:34
Once I had a similar confusion: math.stackexchange.com/questions/64456/how-to-define-infty – gaurav Dec 31 '11 at 17:41

$$\lim_{x \rightarrow \infty}\frac{-1}{\frac{1}{x}}=-\infty$$
$$\lim_{x \rightarrow \infty}\frac{-1}{\frac{1}{-x}}=+\infty$$
Both expressions have the form $\frac{-1}{0}$. You have to know how the lower sequence approaches 0, it can even be that the limit does not exist.