数学中的“反客为主”也称更换主元,是指在解题过程中将两个字母或代数式主次互换,使问题达到消元、降次、化归的目的,将复杂问题简单化.使用这种方法必须抓住问题的实质,要求学生挣脱知识框架的束缚,激活他们的多元思维,创造解题新平台.下面以几道题为例进行说明.例1已知a1,n In mathematics, “anti-offer-based” is also called “replacement of the main element”, which refers to the exchange of two letters or algebraic numbers in the process of solving questions, so that the problem can be eliminated, reduced, and returned to the goal, simplifying the complex issues. Using this method must seize the essence of the problem, requiring students to break away from the shackles of the knowledge framework, activate their diversified thinking, and create a new platform for problem solving. The following uses several examples as an example. Example 1 Known a1,n