守候迈小天2012-11-04TA获得超过1247个赞关注设A(x1,y1),B(x2,y2),M(x0,y0)PAB直线方程为：y-4=k(x-5)因AB在椭圆上：4x1²+5y1²=204x2²+5y2²=20两式相减：4(x1+x2)(x1-x2)=-5(y1+y2)(y1-y2)4(x1+x2)/(y1+y2)=-5(y1-y2)/(x1-x2)=-5K4x0/y0=-5Ky0-4=k(x0-5),K=(y0-4)/(x0-5)所以4x0/y0=-5(y0-4)/(x0-5)整理4x/y=-5(y-4)/(x-5)4x(x-5)+5(y-4)*y=04x²-20x+5y²-20y=0