(x-2)^2+(y-1)^2=4只要找出圆心A(2,1)关于直线的对称点B(a,b)即可AB关于直线对称,则直线AB垂直线x-y+1=0,且AB中点在直线上x-y+1=0斜率是1AB与之垂直则斜率(b-1)/(a-2)=-1a+b-3=0AB中点[(a+2)/2,(b+1)/2]在x-y+1=0上(...