主元法就是在解答含有多个变元的数学问题时,恰当地选择其中一个变元为主要元素,其他变元暂视为常量,将原问题转化为基本问题和基本方法来求解的方法.特别地,可以某一特殊常数为主元.运用这种方法解题,能够培养学生转化的数学思想,现举例说明其解题功能. The principal element method is to properly select one of the variables as the main element when solving a mathematical problem with multiple variables. The other variables are temporarily considered as constants, and the original problem is converted into a basic problem and a basic method to solve the problem. In particular, a special constant can be used as the main element. Using this method to solve problems can train students to transform the mathematical thinking, and now illustrate the problem solving function.