Check the article on the graphic knowledge points of the seventh grade mathematics life plane+February 65438, 2009+Wednesday 0611:131. Polygon: Generally speaking, a polygon is a closed figure surrounded by some end-to-end line segments. We usually divide polygons into triangles, quadrilaterals and pentagons according to the number of sides ... 2.N-polygon: A closed figure surrounded by n end-to-end line segments is called an N-polygon (n is an integer greater than or equal to 3). 3. Polygon segmentation: Starting from a certain vertex of a polygon and connecting this vertex with other vertices respectively, the polygon can be divided into several triangles. 4. There are (n- 3) diagonal lines from a vertex of an n- polygon, and the N-polygon is divided into (n-2) triangles. N polygon * * * has n vertices, n edges and n(n-3)÷2 diagonals. 5. Circle: The figure formed by the rotation of a line segment around one end is called a circle. 6. The line segment between two points on a circle is called an arc, and the figure consisting of an arc and two radii passing through the end points of the arc is called a fan. 7. A circle can be divided into several sectors. 8. Two points on the circle (the line segment connecting the two points is not the diameter) divide the circle into two parts, one part is larger than the semicircle and the other part is smaller than the semicircle, so the two points on the circle are divided into two arcs, and each arc corresponds to a sector.