本文所述的是用刻度尺解决只度量一次的问题 ,此类问题如果不限定度量的次数 ,显然容易解决 ,如果限定只量一次 ,那就需要仔细揣磨 ,认真分析 .图 1　　　　　　　　图 21　通过测量计算长度例 1　如图 1,已知 :△ABC中 ,AB=AC =10 ,P为底边BC上任意一点 ,PE、PF分别垂直AB、AC This article describes the use of a scale to solve problems that are measured only once. If you do not limit the number of measurements, it is obviously easy to solve. If you limit the quantity only once, you need to carefully ponder and carefully analyze. Figure 1 Figure 21 Calculated Length Example 1 As shown in Fig. 1, it is known that: △ABC, AB=AC =10, P is any point on the bottom edge BC, PE, PF vertical AB, AC, respectively