复合函数定义:设y=f(u),u=g(x),则y=[f(x)]叫做y=f(u)与u=g(x)的复合函数。反之,已知复合函数y=[f(x)],若令t=g(x),则y=f(t),而y=f(t)就是y=f(x),即它们是同一个函数,只是表示自变量的字母不同。分析定义可以看出,其蕴涵着换元法思想。通过换元,可以把抽象的复合函数转化为一般函数,从而把抽象的复合函数问题转化为一般函数问题来解决。在挖掘知识的形成 Composite function definition: Let y = f (u), u = g (x), then y = [f (x)] is called the composite function of y = f (u) and u = g (x). On the other hand, the complex function y = [f (x)] is known, and y = f (t) and y = f The same function, only that the different variables of the letters. Analysis of the definition can be seen that it contains the idea of ​​exchange law. By changing yuan, the abstract compound function can be transformed into a general function, so that the abstract compound function problem can be transformed into a general function problem to solve. In the excavation of the formation of knowledge