在一些实际问题中,我们需要求一些不在一条直线上的两条甚至多条线段的和的最小值.轴对称知识在解决这类问题时有很重要的作用.一动点式1.一个动点例1如图1,将军从A地出发到河边(河的边缘线是l)饮马,然后再到B地的军营视察.求作l上一点P,使得PA+PB最短. In some practical problems, we need to find the minimum of the sum of two or more line segments that are not in a straight line. Axisymmetric knowledge plays a very important role in solving this kind of problem. Example 1 In Figure 1, the general departs from Point A to the river where the edge of the river is l, and then inspects the barracks in Area B. Ask for the previous point P, which gives the shortest PA + PB.