人教版的初中《几何》第二册第９１页例３、第９２页练习第３题、第９６页习题第７题三道图１题都可归结为一个数学模型：已知直线ａ和ａ的同侧两点Ａ、Ｂ（图１），求作点Ｃ，使Ｃ在直线ａ上，并且ＡＣ＋ＣＢ最小．这是一个几何极值问题，对学生来讲难点有两个，一是为何... PEP’s junior high school “geometry” second volume of the first 91 pages of the example 3, page 92 practice 3 questions, page 96 exercises the seventh question three questions Figure 1 questions can be attributed to a mathematical model: known straight line a and Two points a and B on the same side of a (Fig. 1), for point C, so that C is on the straight line a, and AC + CB is the smallest. This is a geometric extremum problem. There are two difficulties for students, one is why...