平行四边形有许多重要的性质.在证明某些几何问题时,若能依据题目特点,恰当地添加辅助线构造出平行四边形,不仅可使问题迅速得到解决,而且还可以培养学生思维的独创性.现举例说明.一、证明线段相等例1已知:如图1,在 Parallelograms have many important properties. When we prove certain geometric problems, if we can appropriately add auxiliary lines to construct parallelograms based on the characteristics of the topics, not only can the problems be solved quickly, but also the originality of students’ thinking can be cultivated. Now give an example. First, prove that the line segment is equal to Example 1 is known: as shown in Figure 1,