**
**Vertical:

y = a (x - h)^{2} + k

If "a" is positive the parabola opens up and has a minimum
value.

If "a" is negative the parabola opens down and has a maximum
value.

|a| = 1; normal width

|a| > 1; narrow width (vertical stretch)

|a| < 1; wider width (vertical shrink)

vertex (h, k)

axis of symmetry: x = h

The minimum or maximum is the same as the "y" value of the
vertex.

The vertex is the midpoint between the focus and the directrix.

The
eccentricity of a parabola is the distance from the focus to any point on
the graph divided by the distance from that same point on the graph to the
directrix. Since this the same for a parabola, the eccentricity, e =
1.