几何命题的证明,除极少数的题外都需要添作适当的辅助线,才能完成.但辅助线的添法,千变万化,没有固定的模式,所以是掌握证题方法的一个难点,又是解题的关键,往往有时因添不出辅助线或添得不当使题解不出来或解得非常繁琐,在教学时必须注意培养学生添加合适辅助线的能力,在三角形中经常添加的是哪些辅助线呢?笔者分述如下,以供参考.一、证两角或两条线段相等时,经常添加辅助线造成全等三角形例1如图1所示,已知:△ABC中,AB=AC,在AB Proof of geometric proposition, with the exception of a few questions need to add appropriate auxiliary line in order to complete.But the auxiliary line Tim, the ever-changing, there is no fixed pattern, it is a difficult way to master the Syndrome method, but also the solution The key to the question is that sometimes it is very tedious to get rid of the auxiliary line or improper improper problem sometimes. In teaching, we must pay attention to cultivating the students’ ability of adding appropriate auxiliary lines, which auxiliary lines are often added in the triangle I author points are as follows, for reference.First, the two corners of the card or two line segments are equal, often add auxiliary line resulting congruent triangle Example 1 As shown in Figure 1, known: △ ABC, AB = AC, At AB