焦点坐标F（1，0）直线AB方程为x=y+1设A(x1,y1),B(x2,y2)与y^2=4x联解得到y^2-4y-4=0y1+y2=4y1y2=-4/AB/^2=(1+1)(y1-y2)^2=2[(y1+y2)^2-4y1y2]=2(16+16)=64/AB/=8
