If the tangents at the extremities of a focal chord ofthe parabola x2=4ay meet the tangent at the vertexat points whose abcissac are x1 and x2 then x1x2=

One extremity of the focal chord be 2at,at2 . Equationof the tangent is tx=y+at2 which meets thetangent at the vertex y=0 at x=at so  x1=at and x2=a−1t thus x1x2=−a2.