设圆心（x,y)
2x-y-3=0
(x-5)^2+(y-2)^2=(x-3)^2+(y+2)^2
x=2 y=1
圆心（2,1）半径r^2=(2-5)^2+(1-2)^2=10
方程 （x-2)^2+(y-2)^2=10