a^2=5,b^2=4,c^2=a^2-b^2=1.故左焦点坐标是:F1(-1,0).设弦AB坐标分别是:A(X1,Y1),B(X2,Y2),中点P坐标是(X,Y)那么有:X1+X2=2X,Y1+Y2=2Y又:x1^2/5+y1^2/4=1x2^2/5+y2^2/4=1二式相减得:(x1+x2)(x1-x2)/5+(y1+y2)(y1-y2)...