焦点F(p/2,0),A(x0,y0),B(x0,-y0) AF斜率k1=y0/(x0-p/2) OB斜率k2=-y0/x0 k1*k2=-1 y0^2=x0^2-x0p/2, y0^2=2px0 x0=5p/2, 直线AB垂直于x轴 方程为x=5p/2
