平行线分线段成比例定理(以下简称为定理)是总领关于相似形问题全部内容的纲目性定理,在很大程度上说,影响《相似形》一章教学成败的关键性因素,就取决于该定理教学的优劣。也正由于该定理在《相似形》一章所处的地位如此举足轻重,如何把它教好便一向是几何教学中的热门话题,在几何教法的理论研究方面对它的探讨也相对地显得较多,本文则希望能在扬百家之长并同时避诸家之短的基础上,提出关于该定理教学的一些较为切实易行的设想,以供大家参考,不足之处,尚需各同行在教学实践中继续补正。一、关于定理的证明、扩展和图形的变通 The proportional theorem of the parallel line segment (hereinafter abbreviated as theorem) is an outline theorem about the entire content of the similarity problem. To a large extent, the key factor that influences the success or failure of the teaching of similarity chapter depends on The pros and cons of this theorem. It is because of this theorem that the status of the “similarity” chapter is so important. How to teach it is always a hot topic in the teaching of geometry. The study of geometry teaching method is relatively obvious. More often than not, this article hopes to raise some of the more tangible ideas for teaching the Theorem on the basis of raising the length of one hundred schools and avoiding the shortcomings of homes. For your reference, the inadequacies still require each Peers continue to make corrections in teaching practice. First, the proof of the theorem, extensions and graphics