初中平面几何证明解答题是初中数学的一大难点,而添加辅助平行线是常用方法.常能使久思不得其解的问题呈现“柳暗花明又一村”的局面.下仅举几例,望能达到“领会一例通晓一类”之功效.一、构造三角形的中位线例1已知:如图1所示,在△ABC中,AB=AC,延长AB至D,使BD=AB,E为AB中点,连结CE、CD.求证:CD=2CE. The problem of junior high school plane geometry proof and solution is a major difficulty in junior high school mathematics. Adding auxiliary parallel lines is a common method. It can often make the long-studied problem present the situation of “Yanming Huaming Youyi Village”. Here are just a few examples. , hope to achieve “ understanding an example of a class known ” effect. First, the structure of the triangle in the median line 1 example: As shown in Figure 1, in △ ABC, AB = AC, extend AB to D, so that BD=AB, E is AB midpoint, link CE, CD. Proof: CD=2CE.