设AB方程为y=k(x+a) 抛物线方程y^2=2px 联立得 k^2 x^2 +(2ak^2-2p)x +k^2a^2 =0x1x2+y1y2=0 (1) x1x2=a^2 (2) x1+x2=(2p-2ak^2)/k^2 (3)利用AB方程得y1y2=k^2(x1x2+ax1+ax2 +a^2) 联立得a=-2p定点（2p,0)...