圆过AB则圆心在AB垂直平分线上(-1+3)/2=1,(4+2)/2=3AB中点是C(1,3)AB斜率是(2-4)/(3+1)=-1/2所以AB垂直平分线斜率是-1/(-1/2)=2所以AB垂直平分线是y-3=2(x-1)圆心又在y轴则x=0所以y-3=-2所以圆心D(0,1)则r²=|AD...