椭圆方程：x^2/9+y^2/4=1设此弦与椭圆的两交点坐标分别为(x1,y1)和(x2,y2),分别代入椭圆方程中,得(x1+x2)(x1-x2)/9+(y1+y2)(y1-y2)/4=0即：(x1+x2)/(y1+y2)=-9(y1-y2)/4(x1-x2)设弦中点坐标为（x,y）则x1+x2=2x,y1+y...