换元法就是在解决复杂的数学问题时 ,用变量代换的方法将式子中重复出现的或比较复杂的部分用一个字母或较为简单的式子表示 ,从而达到突出主要矛盾 ,简化解题过程的目的 .换元法是数学解题中的一种重要的思想方法 ,常用在求值域、求最值、求解析式、数列计算、不等式证明、解 The replacement method is to solve the complex mathematical problem by using variable substitution method to represent the repeated or complex part of the formula with a single letter or a simpler formula, so as to highlight the main contradiction and simplify the problem solving. The purpose of the process. The equivalence method is an important method of thinking in mathematical problem solving. It is often used in the evaluation domain, the most value, the analytical formula, the series calculation, the inequality proof, the solution