Answer:

Step-by-step explanation:
We want to find the equation of the parabola with a focus of  and directrix
 and directrix  .
.
Considering the directrix, the quadratic graph must open downwards.
The equation of this parabola is given by the formula,
 , where
, where  is the vertex of the parabola.
 is the vertex of the parabola.
The axis of this parabola meets the directrix at  .
.
Since the vertex is the midpoint of the focus and the point of intersection of the axis of the parabola and the directrix,
 and
 and  .
.
The equation of the parabola now becomes,
 .
.
Also  is the distance between the vertex and the directrix.
 is the distance between the vertex and the directrix.

This implies that  .
.
Since the parabola turns downwards,
  .
.
Our equation now becomes,
 .
.
 .
.
We make y the subject to get,
 .
.
This is the same as 
 .
.