Function convergence criterion: the definition that a function converges to a certain point. For any real number C, there is a number greater than 0, and for any two numbers A and B, the definition that A minus B is greater than 0 and less than C .. converges well reflects the essence of mathematical analysis.
Said:
First of all, we should understand that a function is the corresponding relationship between sets. Then, we should understand that there is more than one functional relationship between A and B, and finally, we should focus on understanding the three elements of the function.
The corresponding rules of functions are usually expressed by analytical expressions, but a large number of functional relationships can not be expressed by analytical expressions, but only by images, tables and other forms.