To explore this definition, investigate the diagram below.
Pick any point on the parabola (say, $\,\text{P}1\,$).
Pick a different point on the parabola (say, $\,\text{P}2\,$).
No matter what point you choose on a parabola,
You can play with parabolas here. 

Parabolas have some beautiful geometric properties
REFLECTING PROPERTY OF PARABOLAS
Rays emanating from the focus will always be reflected perpendicular to the directrix.
To explore this property, investigate the diagram at right.
Place a light at the focus. This ability of parabolas to generate straight, focused beams of light makes them valuable in applications as varied as laser surgery and the Hollywood beams of light! 

This same geometric property also allows parabolas to act as collectors:
Think about the satellite dish on the outside of a house.
Beams enter the dish at all possible angles,
but those that come in perpendicular to the directrix
are all focused on a single point, where a
device collects the signal, amplifies it, and sends it into the house.
Thus, the name focus is appropriate for this special point!
VERTEX OF A PARABOLA
The vertex of a parabola is the point that is exactly halfway between the focus and the directrix.
It is the point where the parabola turns (i.e., changes direction). 

The distance between the focus and the vertex affects the shape of the parabola, as shown below.
As the focus moves farther away from the vertex, the parabola gets wider (flatter).
In any orientation of a parabola, the focus is always inside the parabola. 


On this exercise, you will not key in your answer. However, you can check to see if your answer is correct. 
PROBLEM TYPES:
