Find equation of parabola with focus and directrix

[LeadyKnight]

Homework Statement

Find the equation of the parabola with focus (0, -4) and directrix y = -2

i barely understand this thing. i mean how do i find the vertex.
the book says D1 = focus to any point on the graph, and D2= the point on the graph to the directrix. and D1 = D2. how do i graph if i don't know the vertex

Homework Equations

The Attempt at a Solution

answer: y + 3 = -1/4(x)²

 

[Pastapiggy]

The vertex is the midpoint between the focus and the directrix.