(1)
所求距离=纵坐标为p/2的点到准线的距离
=(p/2)^2/2p-(-2p/4)=5p/8
(2)
P(y0^2/2p,y0),A(y1^2/2p,y1),B(y2^2/2p,y2)
kPA=(y1-y0)/(y1^2/2p-y0^2/2p)=2p/(y1+y0)
kPB=2p/(y2+y0)
αPA+αPB=π
tan(αPA)=tan(π-αPB)=-tan(αPB)
kPA+kPB=0
2p/(y1+y0)+2p/(y2+y0)=0
y2+y0+y1+y0=0
(y1+y2)/y0=-2
kAB=(y2-y1)/(y2^2/2p-y1^2/2p)
=2p/(y1+y2)
=-p/y0为非零常数