这个属于点差法.设A(x1,y1),B(x2,y2),则2x0=x1+x2,2y0=y1+y2A,B在椭圆上,x1^2/a^2+y1^2/b^2=1 -----------------(1)x2^2/a^2+y2^2/b^2=1 -----------------(2)(1)-(2)(x1-x2)(x1+x2)/a^2+(y1-y2)(y1+y2)/b^2=0即2(x1...