The parabola is therefore symmetrical about a vertical axis.

As the focus is below the directrix, the parabola opens downwards, and will have an equation of the form:

(x – h)^2 = 4a(y – k) ……(1)

where (h, k) is the vertex and 2a is the distance from the focus to the directrix. For a parabola opening downwards, a is negative.

The y co-ordinate of the vertex is half way between that of the focus (-1) and that of the directrix (5), and is therefore (5 – 1)/2 = 2.

The x co-ordinate of the vertex is the same as that of the focus, namely 3. The vertex is therefore (3,2).

Substituting the vertex co-ordinates in (1) gives the equation:

(x – 3)^2 = -12(y – 2).