Definition
Let f(x) be a function of x. If for every positive number ε ( tends to 0),
then there exist a positive number δ such that whenever
0 < | x - a |< δ => | f(x) - l | < ε ,
then we can say , f(x) tends to limit l as x tends to a
and we can write
lim (x→a) f(x) = l.