易求得左焦点为(-2,0) ∴抛物线方程为y^2=-8x 设弦与抛物线交点分别为（x1,y1) (x2,y2)　　则y1^2=-8x1 y2^2=-8x2 两式相减 得(y1+y2)(y1-y2)=-8(x1-x2)即y1-y2/x1-x2=-8/y1+y2 ∵y1-y2/x1-x2=k 且y1+y2/2=-1∴k=-8/...