何以点可以视为圆？周传忠（华南师范大学５１０６３１）我们知道，若曲线ｌ：ｆ（ｘ，ｙ）＝０和ｋ：ｇ（ｘ，ｙ）＝０相交，则方程ｆ（ｘ，ｙ）＋λｇ（ｘ，ｙ）＝０表示通过这些交点的一个曲线系．利用这一结论来解一些问题常是很方便的．文［１］、［２］更提出，可以... Why can a point be considered a circle? Zhou Chuanzhong (South China Normal University 510631) We know that if the curves l:f(x,y)=0 and k:g(x,y)=0 intersect, the equation f(x,y)+λg(x,y)= 0 represents a curve through these intersections. It is often convenient to use this conclusion to solve some problems. Articles [1], [2] are more proposed, can...