If the vertex of the parabola is at (0, 0) and the focus is (0, -4) <em>which is 4 units down</em><em> </em>then the directrix will be the line 4 units UP.
Answer: y = 4
<u>Equation of parabola:</u>
; where p is the distance from the vertex to the focus.
As stated above, the focus is 4 units down, so p = -4