当弦PQ不垂直X轴时,设PQ方程为y=k(x-p),代入y^2=2px得k^2(x-p)^2=2px,整理得k^2x^2-2p(1+k^2)x+p^2k^2=0设根为x1,x2,则(x1-p)^2=2px1/k^2,(x2-p)^2=2px2/k^2且x1+x2=2p(1+k^2)/k^2,x1x2=p^2则P(x1,y1),Q(x2,y2)则MP^...