梯形问题的常用辅助线

The lines of help on ladder-shaped problems

针对不少学生在解平面几何问题时缺乏作辅助线的经验 ,就梯形问题的几种常用辅助线作法作了介绍 ,并说明了各种作法的目的、一般适用的条件以及分析问题的方法。

We often make the lines of help when we work on plane geometry.In view of students' lack of experience to make the lines of help,this article introduces several methods to make lines of help on ladder shaped problems and gives examples to explain each method to improve the ability of analysing problems.