在平面几何中,证明两直线垂直的问题不少,如果我们能帮助学生在掌握基础知识的同时,灵活变通,归纳一些证题方法,那么,此类问题的教学效果,必将显著提高。下面就两直线垂直的证明问题,谈谈证明的一些基本方法。一、利用三角形内角和定理。先证明三角形中的两角之和为90°,则可知第三角为直角。例1 在(?)ABCD 中,AD=2AB,延长 AB 到 F,使 BF=AB,又延长 BA 到 E,使 AE=AB,连结 EC 交 AD 于 G,连结 FD交 BC 于 H、交 EC 于 O. In plane geometry, there are quite a few problems proving that the two straight lines are vertical. If we can help students master the basic knowledge while flexibly adapting and summarizing some of the proof methods, the teaching effect of such problems will surely increase significantly. The following two vertical lines to prove the problem, to talk about some of the basic methods to prove. First, the use of triangular interior angles and theorems. First prove that the sum of the two corners of the triangle is 90 °, we can see that the third corner is a right angle. Example 1 In (?) ABCD, AD = 2AB, extend AB to F, make BF = AB, extend BA to E, make AE = AB, connect EC to AD in G, At