一、直接利用定义梯形:一组对边平行,另一组对边不平行的四边形.根据这个定义,要说明一个四边形是梯形,必须具备两个条件:①一组对边平行,②另一组对边不平行.例1如图1,在△ABC中,AB=AC,BD、CE分别为∠ABC、∠ACB的平分线,试说明四边形EBCD为等腰梯形.分析四边形EBCD中,BE与CD相交于点A,这两边不平行,要说明四边形EBCD为等腰梯形,只要设法说明:①DE∥BC,②BE First, the direct use of the definition of trapezoid: a group of parallel to the other side of the group is not parallel to the quadrilateral.According to this definition, to indicate a quadrilateral is trapezoidal, must have two conditions: ① a group of parallel to the other side ② another Group 1 is not parallel to the side of the case Example 1 Figure 1, △ ABC, AB = AC, BD, CE were 平ABC, ∠ ACB bisector, try to illustrate the quadrilateral EBCD isosceles trapezoid. And CD intersect at point A, the two sides are not parallel, to illustrate the quadrilateral EBCD isosceles trapezoid, as long as trying to explain: ① DE∥BC, ② BE