Let the green point on the parabola be P.
Let the focus of the parabola be F.
Let M be the point on the directrix where the perpendicular from P intersects.
We know that for a conic, [tex]\frac{FP}{PM}=e[/tex] and for a parabola, e = 1.
So, [tex]\frac{FP}{PM} =1[/tex]
FP = PM
It is given that the distance between the green point and the focus is 9.
That is, FP = 9.
So, PM = 9.
Hence, the distance between the green point and the directrix = 9.
