On this platform, for those who have just finished learning the two chapters of Set and Function in Grade One, they always don't understand the most basic and simple questions and don't know what is going on. The first is the definition of function: A and B are two groups of non-empty numbers, and a mapping from set A to set B is called a function from set A to set B. We write it as y=f(x), x∈A, y∈B, where set A is the domain, usually represented by the letter D, d is the range of value of x, and set B is the range of value. After understanding the definition of function, let's give an example. For function f(x), the domain is the value range of x, and for function f(g(x)), the domain of function f(x) is the value range of g(x), that is to say, the domain of f(x) and the value range of g(x) are the same. This type of question grasps two points: ① Under the same mapping F, the contents in brackets are always the same as the definition domain of f(x). No matter how complex the expression is, the domain must be the range of X. The topic is the domain of f(x- 1) (1, 2). (2), f(x- 1) field (1, 2) indicates that the value range of x is 1