在中学数学中,换元法是一个很重要的数学思想方法。它常能使问题由繁化简,由难化易,在函数问题中,常常要对自变量实施某种代换,函数问题中的代换法的基本思想是:将函数中的自变量适当地代换成别的自变量,得到一个新的函数关系式,将它与原函数关系联立,解出其中的一个函数,必要时再作代换,便可得到所求的函数解析式。在代换时,要力求使函数的定义域不发生变化。下面举例说明: In middle school mathematics, changing yuan method is a very important mathematical thinking method. It often makes the problem simple and easy, easy to change, in function problems, often to implement some kind of substitution on behalf of variables, the basic idea of ​​the substitution method in the function of the problem is: the arguments in the function appropriate A new function relation is obtained, which is combined with the relation of the original function to solve one of them. If necessary, it can be replaced, and then the analytical function of the function can be obtained. In the substitution, we must strive to make the function of the domain does not change. Here’s an example: