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1.存在的问题.人教版数学教科书七年级下册第79页的多边形的概念如下:类似的,在平面内,由一些线段首尾顺次相接组成的图形叫做多边形.2.两个问题的比较.人教版数学教科书七年级下册第63页的三角形的概念如下:由不在同一条直线上的三条线段首尾顺次相接所组成的图形叫做三角形.可以看到这两个概念中相差“不在同一直线上”的条件.3.问题的思考.三角形的概念中有了这样的条件,那么在多边形的概念中到底要不要这个条件呢?以四边形为例:如图:AC线段以A为首以C为尾,CD线段以C
1. Existing problems The concept of polygons on page 79 is as follows: Similarly, in the plane, by the end of the line is connected to form a graphic called polygons .2. Two problems The concept of a triangle on page 63 is as follows: A graph composed of three line segments that are not on the same straight line is called a triangle, and you can see that in these two concepts The difference between “not in the same line ” conditions .3 thinking of the problem .Third concept has such a condition, then the concept of polygons in the end whether or not this condition? The quadrangle as an example: Figure: AC Line to A as the first C to the tail, CD line to C