一、教学中的两次重创学习完全等三角形的性质和判定,我决定补充几何证明中添加常见辅助线的方法,结合刚学的三角形的三条重要线段,我把有关中点问题采用的“倍长中线法”放到首位。于是,我选了下面的例题:例1.已知:如图1,在△ABC中,AB≠AC,D、E在BC上,且DE=EC,过D作DF交AE于点F,DF=AC。求证:AE平分∠BAC First, the two heavy learning in teaching completely triangular nature and judgment, I decided to add geometric proof of the common way to add a supplementary line, combined with just learning the triangle of the three important lines, I put the question about the midpoint Double long method "to the first place. Thus, I chose the following example: Example 1. Known: As shown in Figure 1, in ABC, AB ≠ AC, D, E in BC, and DE = EC, DF = AC. Prove: AE bis ∠ BAC