1/x

does tend to −

as you approach zero from the left, and 

That these limits are not equal is why 1/0 is undefined.

In Calculus sometimes we write

10+=+,

10−=−,

This notation makes 10 sometimes + and sometimes− , but you have to be careful what it means. It doesn't literally mean 10 , it's actual meaning in Calculus is

a limit of the type f(x)g(x) , where limf(x)=1 and limg(x)=0 .

While writing 10 is much more convenient than writing that expression, it has the downside that many people take it to mean literary 1 divided by 0 .

Sometimes in calculus 10 is + , sometimes it is − and sometimes it doesn't exists. But while the meaning is somehow closed to the idea of 10 , in calculus 10 means something else that division.

After reading few post on this we came to know that it depends on the context of its use.

Actually what happens is more subtle. In two different areas of mathematics that notation is used to denote two different things. When you say 10 , if you mean standard division of real numbers, then that is not defined, no matter what the context is...

There are actually many situations when the unfortunate use of the same notation/definition for different things creates confusion....