对于实数x,y有不等式x2+y2≥2xy,其中当且仅当x=y时取等号,应用这一等号成立的条件来解一些诸如求最值、值域等问题,有时显得简洁、轻快,能收到化难为易、事半功倍之效.但一定要注意题目中存在的某些隐含条件,否则极易产生错误,且不易觉察,笔者结合多年的教学实践,谈一点体会,以引起同学们的注意. For a real number x, y has an inequality x2+y2≥2xy, where if and only if x=y is an equal sign, apply the condition that the equal sign is established to solve some problems such as finding the maximum value, value range, etc. , brisk, can receive hard work, easy and effective, but must pay attention to the existence of some implicit conditions, otherwise it is easy to produce errors, and not easy to detect, the author combines many years of teaching practice, talk a little experience to Cause the attention of the students.