（一）知识要点本单元的主要内容可分为三大部分：多边形的概念和性质；平行四边形、矩形、菱形、正方形的定义、性质、判定；梯形的定义、性质和判定．重点是平行四边形和梯形的定义、性质、判定及应用．一、多边形的有关概念和性质1．多边形的定义在平面内，由n（npe3）条线 (I) Knowledge points The main contents of this module can be divided into three parts: the concept and nature of polygons; the definition, nature, and determination of parallelograms, rectangles, diamonds, squares; the definition, nature, and determination of trapezoids. The emphasis is on the definition, nature, determination and application of parallelograms and trapezoids. First, the concept and nature of polygons The definition of the polygon is in the plane, from the n(npe3) line