Question

what is the name of the line that you use to define a parabola?
a. parallel
b. focus
c. perpendicular
d. directrix

Explanation:

A parabola is defined as the set of all points that are equidistant from a fixed - point (the focus) and a fixed - line (the directrix). The line used in its definition is the directrix.

Answer:

D. Directrix