For what values of "a" will the tangents drawn to parabola y^2 = 4ax from a point not...

[Clereamus Jd]

...on Y-axis be normal to :? normal to: the parabola x^2 = 4y
answer is a < - 2?2 or a > 2?2 but i dont know how to get it..................plz help.............thanx