一、问题提出:苏科版实验教科书九年级上册第一章第39页《图形与证明二·复习题》第14题如下(图1):三个城市A、B、C分别位于一个等边三角形ABC的三个顶点处,要在这三个城市之间铺设通信电缆,现设计了三种方案:(1)连接AB、BC;(2)连接BC,连接点A与BC的中点D;(3)找出到△ABC三个顶点距离相等的点 First, the question raised: Suke version of experimental textbook ninth grade first chapter on page 39 “graphics and proof two review questions” as follows (Figure 1): three cities A, B, C are located on one side At the three apexes of the triangle ABC, three communication schemes are to be laid between the three cities: (1) connect AB and BC; (2) connect BC and point A and the midpoint D of BC ; (3) Find the point where the distance between the three vertices of △ ABC is equal