x^2/a^2+y^2/b^2=1(a>b>0)设点M(x1,y1)N(x2,y2)再将MN点坐标带入标准方程得x1^2/a^2+y1^2/b^2=1x2^2/a^2+y2^/b^2=1然后两式做差得x1-x2/y1-y2=-b^2(x1+x2)/a^2（y1+y2)然后k=-b^2/a^2*MN的中点坐标K为直线的斜
