x^2+y^2+ax+by+e=0x^2+y^2+cx+dy+f=0假设两圆交点(x1,y1)(x2,y2)那么x1^2+y1^2+ax1+by1+e=0x1^2+y1^2+cx1+dy1+f=0两式相减(a-c)x1+(b-d)y1+e-f=0同理(a-c)x2+(b-d)y2+e-f=0可知(x1,y1)(x2,y2)一定在直线(a-c)x+(b-d)y+e-f=0上显然通过两点的直线只有一条 即直线方程唯一相交的直线即为(a-c)x+(b-d)y+e-f=0