在近几年的初中数学竞赛中,常出现一些有关方程、不等式、极值等问题,这些问题若直接求解,往往会遇到困难,但若能注意构造一个适当的二次函数,借助于函数的有关性质来求解,则会收到意想不到的效果,请看下面几例。 In the junior high school math competition in recent years, there are often problems concerning equations, inequalities, and extremes. If these problems are solved directly, they often encounter difficulties, but if you can pay attention to construct an appropriate quadratic function, with the help of The nature of the solution to the problem, you will receive unexpected results, see the following examples.