Objective To write the equation of a parabola and to graph parabolas
Parabolas
From Chapter 4, you know that a parabola has a vertex and an axis of symmetry. A parabola also has other characteristics.
Essential Understanding Each point of a parabola is equidistant from a point called the focus and a line called the directrix.
Definition
A parabola is the set of all points in a plane that are the same distance from a fixed line and a fixed point not on the line.
The fixed point is called the focus of a parabola.
The fixed line is called the directrix.
The distance between the vertex and the focus is the focal length of the parabola.
Graph
In this lesson, you will consider vertical parabolas (each of which has a vertical axis of symmetry and a horizontal directrix) and horizontal parabolas (each of which has a horizontal axis of symmetry and a vertical directrix).