Question

1.已知圆心为C的圆经过点A（1,1）和B（2,-2）,且圆心C在直线1：x-y＝-1上,求圆心为C的圆的标准方程.

Answer 1

圆心C在直线1：x-y＝-1上

x=y-1

C(a-1,a)

AC^2=BC^2=r^2

(a-1-1)^2+(a-1)^2=(a-1-2)^2+(a+2)^2

a=-2

C(-3,-2),r^2=25

(x+3)^2+(y+2)^2=25