几何的证明题往往需要添加辅助线,但在什么情况下添加以及如何添辅助线是大家困扰的问题,以下针对三角形和梯形中常用的辅助线加以说明.1.三角形中的辅助线(1)遇到中线——延长一倍若△ABC的中线是AD,可以倍长中线到点E,连接BE,得到△ADC≌△EDB.例1如图1,AD是BC边上的中线,AF=EF,求证:AC=BE. Geometrical proof questions often need to add auxiliary lines, but in what circumstances and how to add auxiliary lines is the problem we are confused, the following for the triangle and trapezoid commonly used auxiliary lines to illustrate 1. Aid in the triangle (1) If the middle line of ABC is AD, you can double the middle line to point E and connect BE to get △ ADC ≌ △ EDB. Example 1 As shown in Figure 1, AD is the center line on the edge of BC, AF = EF, confirmation: AC = BE.