说到数学里的四边形,要从多边形说起。一般地说,在平面上,由不在同一条直线上的几条线段顺次首尾相接所组成的图形叫做折线。如果一条折线的首尾两个端点重合,那么这条折线叫做封闭折线。封闭折线所围成的图形叫做多边形。组成一个多边形的各条线段,叫做多边形的 Speaking of mathematics in the quadrilateral, to start with the polygons. In general, in the plane, by a few lines are not in the same straight line after the end of the series consisting of a graphic called the polyline. If the end of a polyline coincides with the two endpoints, then this polyline is called a closed polyline. The figure enclosed by the closed polyline is called a polygon. The lines that make up a polygon are called polygons