易得焦点坐标F1(-1,0)
设AB所在直线：y=k(x+1)
联立椭圆：(1+k²)x²+4k²x+2k²-2=0
设A(x1,y1),B(x2,y2)即x1+x2=-4k²/(1+k²),y1+y2=k(x1+k2)+2k=-4k³/(1+k²)
AB中点M(-2k²/(1+k²),-2k³/(1+k²))
AB的垂直平分线:y=-(x-m)/k
导入M点坐标M(-2k²/(1+k²),-2k³/(1+k²))
进行求值即可我很笨，怎么样求值？-,-化简很麻烦，呵呵