在解题实践中,我们经常把常数用适当的表达式替换,从而改变题目结构,最终促成问题的解决.这是一种以退为进的解题策略,本文称之为常量替换法.该法主要应用于求最值、证明不等式等题型中,有时也可用于证明等式、求解解析几何问题等场合.下面通过例子说明该法的应用. In the practice of solving problems, we often replace the constants with appropriate expressions, so as to change the structure of the problem and finally to solve the problem. This is a retreat-based problem solving strategy, which we call the constant replacement method. Law is mainly applied to find the most value, proof of inequality and other types of questions, and sometimes can also be used to prove the equation, solve the analytic geometry problems, etc. The following examples illustrate the application of the law.