Question

A parabola can be drawn given a focus of (0,−6) and a directrix of y=−2. Write the equation of the parabola in any form.

Answer 1

Answer:

y = x^2 - 4

Step-by-step explanation:

The vertex of a parabola is exactly halfway between the focus and the directrix.  If the focus is at (0, -6) and the directrix is the line y = -2, then we do this to locate the vertex:  Draw a vertical line through (0, -6) also crossing the line y = -2.  The y value halfway between y = -6 and y = -2 is y = -4, and the vertex is thus (0, -4).

Using the vertex method, write out the equation of this parabola, starting with the general form y - k = (x-h)^2, where (h, k) is the vertex.  Here h = 0 and k = -4

We get:  y + 4 = (x - 0)^2, or y + 4 = x^2, or y = x^2 - 4.  As a check, let x = 0; y = -4, which is the y-coordinate of the vertex.