焦点F(0.5p,0)
抛物线:y^2=2px上任意一点M,MF中点P(x,y)
xM+xF=2xP,xM=2xP-xF=2x-0.5p
yM+yF=2yP,yM=2yP-yF=2y
(yM)^2=2p(xM)
(2y)^2=2p(2x-0.5p)
中点的轨迹方程是抛物线:y^2=p*(x-0.25p)