问题
选择题
已知圆x2+y2+Dx+Ey+F=0的圆心在y轴上，则必有（ ）
A．D=0
B．E=0
C．F=0
D．D=0，且E=0
答案
由圆的方程化为标准方程得：(x-
)2+(y-D 2
)2=E 2
，D2+E2-4F 4
得到圆心坐标为（
，D 2
），因为圆心在y轴上，E 2
所以
=0即D=0．D 2
故选A．
搜题请搜索小程序“爱下问搜题”
已知圆x2+y2+Dx+Ey+F=0的圆心在y轴上，则必有（ ）
A．D=0
B．E=0
C．F=0
D．D=0，且E=0
由圆的方程化为标准方程得：(x-
)2+(y-D 2
)2=E 2
，D2+E2-4F 4
得到圆心坐标为（
，D 2
），因为圆心在y轴上，E 2
所以
=0即D=0．D 2
故选A．
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