椭圆x^2/a^2 + y^2/b^2 =1 在顶点(a,0)处的曲率半径为b^2/a,在(0,b)处的曲率半径为a^2/b.
双曲线x^2/a^2 - y^2/b^2 =1在顶点(a,0)或(-a,0)处的曲率半径都是b^2/a.
抛物线y^2=2px (p≠0)在顶点(0,0)处的曲率半径为|p|.