题目不是很明白,你题目应该错了,可把右边的移到左边,分别分解x,y的式子即可,
(x-(x1+x2)/2)^+(y-(y1+y2)/2)^=((x1-x2)^+(y1-y2)^)/4
(x-(x1+x2)/2)^- (x1-x2)^/4+(y-(y1+y2)/2)^-(y1-y2)^)/4=0
((x-(x1+x2)/2) + (x1-x2)/2) *((x-(x1+x2)/2) - (x1-x2)/2)+((y-(y1+y2)/2) +(y1-y2)/2)* ( (y-(y1+y2)/2) -(y1-y2)/2)=0
化简得：（x-x1)(x-x2)+(y-y1)(y-y2)=0