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一.什么叫做线画线画是由有限个点和有限条线所组成的图形,图形中的点叫做线画的顶点,线叫做线画的边;作为线画,则图形还必须满足这样几个条件:1)每个顶点至少是一条边的端点,2)每条边都有两个顶点(可以重合)作为端点(因此每条边都是直线段或者曲线段,3)各条边都不自行相交也不彼此相交。平面几何和立体几何中所遇到的很多由点和线组成的图形都是线画,但是上述三个条件把某些图形排除了出去。条件1)是说线面中不能有孤立的顶点;条件2)是说线画中的边必须有端点(因此直线或者圆都不是线画),也不能只有一个端点(因此射线也不是线画),这时必须注者,两个端点可以重合(因此圆和圆
1. What is called a line drawing line drawing is a figure composed of a finite number of points and a finite number of lines. The point in the figure is called the vertex of the line drawing. The line is called the edge of the line drawing. As a line drawing, the figure must also satisfy such a few lines. Conditions: 1) Each vertex is the endpoint of at least one edge, 2) Each edge has two vertices (can be coincident) as endpoints (so each edge is a straight line or curve segment, 3) Each edge is Do not intersect or intersect with each other. Many of the graphics consisting of dots and lines encountered in plane geometry and solid geometry are line drawings, but the above three conditions exclude certain graphics. Condition 1) means that there can be no isolated vertices in the line surface; Condition 2) means that the edges of the line drawing must have endpoints (thereby the line or the circle is not a line drawing), nor can there be only one endpoint (therefore the rays are not line drawings ), which must be noted at this time, the two endpoints can be coincident (hence the circle and the circle