x^2+y^2+6x-4=0 (1)x^2+y^2+6y-28=0 (2)解得y=x+4,代入(1)解得x=-1 y=3x=-6 y=-2圆心坐标：x0=(-1-6)/2=-7/2y0=(3-2)/2=1/2r^2=[(-2-3)^2+(-6+1)^2]/4=25/2圆的方程为(x+7/2)^2+(y-1/2)^2=25/2
(x-1/2)(x-1/2)+(y+7/2)(y+7/2)=89/2
