Generally speaking, we have the concept of function: let 4 and 8 be non-empty number sets, if they correspond in some way? The related person makes any number x in set 4 uniquely determined in set B? The number/"(x) corresponds to it, so we call 84tb a function from set 4 to set b? (function), written as: y-/(x), xe a.

Generally speaking, we have the concept of mapping: let 4 B be two non-empty sets, if it is determined by one? Correspondence, so that any element in set A is unique in set B? If the determined element Y corresponds to it, then the corresponding "A-B is from set 4 to set B? A map.

Generally speaking, the maximum value of a function is/,and if there is a real number m, it satisfies: (1) For any% ei, there is f (x).