我们知道,线段垂直平分线上的点到线段两端的距离相等,反之,到线段两端距离相等的点在这条线段的垂直平分线上,线段垂直平分线的这两个特征在处理有关线段或角的问题时运用十分广泛,现举例说明.例1如图1,等腰△ABC中,AB=AC,AB+BC=13,AB边的垂直平分线MN交AC于点D,求△BCD的周长 We know that the distance from the point on the vertical bisector of the segment to the end of the segment is equal, whereas the point at the two ends of the segment is equal on the perpendicular bisector of the segment, and these two characteristics of the vertical bisector of the segment are dealing with the relevant segment. The problem of angles or angles is very extensive and is now illustrated by examples. Example 1 is shown in Figure 1. In isosceles △ABC, AB=AC and AB+BC=13, the perpendicular bisector AB of AB side crosses AC at point D. The perimeter of BCD