我们先来看一种分类作等腰三角形的方法. 如图1,已知线段BC,求作△ABC,使△ABC是等腰三角形. 显然,此题答案有无数多个,具有开放性,概括起来有如下三类: (1)若点A为顶点,则点A在线段BC的中垂线上(如图2,BC的中点除外). (2)若点B为顶点,则点A在以B为圆心,BC为半径的圆上(如图3,直线BC与 Let us first look at a method for classifying isosceles triangles. As shown in Figure 1, the known line segment BC is calculated as △ABC, so that ΔABC is an isosceles triangle. Obviously, there are numerous and open answers to this question. To sum up, there are the following three types: (1) If point A is a vertex, point A is on the line perpendicular to the line BC (except for the middle point of BC in Fig. 2). (2) If point B is a vertex, then the point A is on a circle with B as its center and BC as its radius (Figure 3, straight line BC and