Let f be a function.
If f(x) is defined for all real value of x in a neighbourhood of a fixed number 'a'and f(x) approach a fixed number 'L' as x approaches 'a' from either side of a,then 'L' is called the limit of f as x--->a and we write:
limf(x)=L or Ltf(x)=L
x-->a x-->a