y^2=8x的准线,x=-2
圆心C在抛物线y^2=8x上,C(8a^2,8a)
圆C与抛物线的准线相切,r=2+8a^2
圆C过坐标原点:r^2=(xC)^2+(yC)^2=(8a^2)^2+(8a)^2
r^2=(8a^2)^2+(8a)^2=[(8a^2)+2]^2
a^2=1/8
8a^2=1,8a=±8√(1/8)=±2√2
C(1,±2√2)
r=2+8a^2=2+1=3
圆的方程有两个:
(x-1)^2+(y±2√2)^2=9