The focus of a parabola is at and its directrix is the line

MATHEMATICS · Subjective · CBSE · Mathematics · Conic Sections · Conic Sections

Problem

The focus of a parabola is at

(0,-4)

and its directrix is the line

y=4

. Without calculating the full equation, determine whether the parameter

a

in the form

x^{2}=4ay

is positive or negative. Give a brief reason for your answer.