X ^ 2 = 4Y, the tangent of line L passing through a and B is L1 and L2 (1) Verification of L1 vertical L2 (2) It is proved that the focus of L1 and L2 is on the directrix

X ^ 2 = 4Y, the tangent of line L passing through a and B is L1 and L2 (1) Verification of L1 vertical L2 (2) It is proved that the focus of L1 and L2 is on the directrix

(1) ∵ the line L intersects with the parabola x ^ 2 = 4Y at two points, and∵ the line L has a slope, so that its slope is K. from the parabola equation x ^ 2 = 4Y, the coordinates of its focus f are (1,0), ∵ the equation of the line L is y = KX + 1. ∵ A and B are on the line y = KX + 1, ∵ the coordinates of a and B can be respectively (m, KM + 1), (n, K