研究梯形问题时 ,常常需要添加适当的辅助线 ,从而把梯形转化成三角形、矩形或平行四边形 .现列举梯形问题中几种常见辅助线的添法 ,供同学们学习时参考 .一、移动一腰例 1　如图 1,已知梯形ＡＢＣＤ中 ,ＡＢ∥ＣＤ ,以ＡＤ和ＡＣ为边作平行四边形ＡＣＥＤ ,ＤＣ的延长线交ＢＥ When studying trapezoidal problems, it is often necessary to add appropriate auxiliary lines to convert the trapezoids into triangles, rectangles, or parallelograms. Now we will add some common auxiliary lines in the trapezoidal problem to provide reference for students to learn. One is to move one. Waist Example 1 As shown in Figure 1, known trapezoid ABCD, AB ∥ CD, with AD and AC sides as parallelogram ACED, DC extension line to BE