五点定位的二次曲线类型

CLASSIFICATION OF QUADRATIC CURVES DETERMINED BY FIVE POINTS

文章通过二次点列的射影构成，明确说明由平面上任三点不共线的五点，一定可唯一确定一条非蜕化的二次曲线，进而用射出变换法判定了该二次曲线的具体类型，这不仅有助于此曲线的图解，同时也为由定位条件确定的二阶曲面类属的判断提供了有效途径．

In this paper, using the projective structure of range of paints of the second,atuther had proved that five points in a plane, any three of them aren’t on the same line,can determine a proper conic, and had determied the proper conic classification, through the projective transformation. This is not only usefull for the qraphical solition of it’s curves.Furthermove, may give the conicoid classification, this conicoid is determined by nine points in a spare.