解;设直线AB的方程是:y=2x+b抛物线的焦点坐标是(2,0)b=-4y=2x-4直线与抛物线的交点坐标是(x1,y1),(x2,y2)联立方程y=2x-4y^2=8x(2x-4)^2=8x4x^2-16x+16=8x4x^2-24x+16=0x^2-6x+4=0x1=3+根号5x2=3-根号5y1=2+2根号5y2=...