抛物线y²=-8x设弦与抛物线交点A（x1,y1）B（x2,y2）则y1²=-8x1y2²=-8x2两式相减y1²-y2²=-8(x1-x2)(y1-y2)(y1+y2)=-8(x1-x2)根据题意y1+y2=2设直线上任意一点为（x,y）则(y-1)/(x+1)=(y1-y2...