请同学们回顾一下,凸n边形的内角和公式S_n=(n-2)·180°是如何推导出来的?推导公式的指导思想是把求多边形的内角和问题转化为求三角形的内角和问题,“转化”的办法是将多边形分割为若干三角形,由于分割多边形有多种方法,所以推导多边形内角和的方法也有多种。 (1)在图1中,由n边形的某个顶点引对角线,将n边形分成(n-2) Ask the students to review how the interior angle of the convex n-gon and the formula S_n=(n-2)·180° are derived. The guiding idea of ​​the derivation formula is to convert the interior angle and the problem of the polygon to the interior angle of the triangle. The problem, the “transformation” approach is to split the polygon into a number of triangles. Since there are many ways to split a polygon, there are many ways to derive the interior angles of a polygon. (1) In Fig. 1, a vertex is drawn from a vertex of an n-gon, and the n-gon is divided into (n-2)