两个对称点设为A(x1,y1) B(x2,y2) 中点M(x,y)有2x=x1+y1 2y=y1+y2①首先M在直线y=kx+2上,其次AB和直线垂直x1²/4+y1²=1x2²/4+y2²=1两式相减并移项(x1+x2)(x1-x2)/4=-(y1+y2)(y1-y2)(y1-y2)/(x1-x2)=-(x1+x2)/4(y1+y2)等式左边是AB的斜率为-1/k,右边用①式代换于是-1/k=-x/4y再加上y=kx+2联立方程得到x=-8/(3k)y=-2/3M点在椭圆内部,要求x²/4+y²4√5/5或者k