棋子总数=n2
今天你学到了什么？
从简单开始，有序思考 用化繁为简，找到规律
复杂的问题要善 于退， 足够地退，
退到最原始而不 失去重要性的地 方，
是学好数学的一 个诀窍。
不足之处，恳请大家给予批评指正
多边形
边数 内角和
3
4ቤተ መጻሕፍቲ ባይዱ
5
6
180° 360° 540° 720°
（1）多边形内角和与它的边数有什么关系？ 多边形内角和＝（边数-2）×180°
多少次？
1+2+3+...…+39
1+2+3+...…+39
=（1＋39）×19＋20
=40×39÷2
=780（次）
=780（次）
答：40个同学一共要握手780次
同学们，在我们生活中有许多看 似复杂的问题，我们都可以尝试从 简单问题去思考，逐步找到其中的 规律，从而来解决复杂的问题。
举一反三
××
每幅图各有多 少个棋子？
1
4
9
16
问题 在数的过程中，你发现了什么？
1
4
9
16
1×1 2×2
3×3
4×4
每行的棋子数×行数＝棋子总数
问题 1. 第7幅图有多少个棋子？第15幅图呢？ 7×7＝49（个） 15×15＝225（个） 2.第n幅图每边有多少个棋子？一共有多少个 棋子 ？
每行有n个，有n行
34
C
B
also lack the necessary understanding.Two is the business foundation is not solid, the text level is not high. Their work in the army before, although the understanding of the material, but also just only know fur, text level, writing ability is still in a low level interface. The knowledge is not complete, especially it is very little about professional some departments know knowledge, to write Chinese but not false, sometimes rely on online writing or presentation of ready-made one-sided materials, unwilling to make a deep thinking, put all sorts of things together, the presentation quality is not high, due to the overall quality of their own quality is not high, the leadership of departments can not understand, it is difficult to stand in the perspective
