(1)设方程:(x-a)^2+(y-b)^2=r^2
将A、B代入上式:a=b
又:a+b-2=0,a=b=1
A点和圆心坐标求r=2
(x-1)^2+(y-1)^2=4
(2)(x-1)^2=4-(y-1)^2>=0,-1