Even though it might appear a crowded graph I think all of these graphs on the same pages help illustrate a few good points.  For example it is easy to point out the behavior of the tradition c value of the quadratic.  All of these have the c value as negative or positive three.  It is also easy to see how the graph has tremendous symmetry.  The zero's of all the graphs that go through the same points for the graphs that are negatives of each other.  What I mean by negatives is the coefficient values all are opposites.  You can also note that the graphs that have the x coefficient opposite each other are also symmetric over the y axis.