平行线是初中几何的一个重要内容,是进行几何证明的起始课,对学好几何有深远影响.在这章学习中,经常会遇到一些看似较难的几何题,运用某个几何图形的结论后,问题便迎刃而解,显示出强大的优势.下面,介绍一个平行线的基本图形.一、命题及证明命题如图1,已知AB∥CD,求证:∠BED=∠B+∠D.A C D E B图1%证法1用平行线的性质在∠BED内,过E点作射线EF∥AB, Parallel lines are an important part of junior high school geometry and are the initial lesson for geometric proof. They have far-reaching influence on the learning of good geometry. In this chapter, we often encounter some seemingly difficult geometric problems, using a geometry The problem will be solved, showing a strong advantage. Here, the basic graphics of a parallel line. First, the proposition and proof of proposition Figure 1, known AB ∥ CD, verify: ∠ BED = ∠ B + ∠ DA CDEB Figure 1% card law 1 with the nature of the parallel lines in the ∠ BED, over E point for the ray EF∥ AB,