What does each of the coefficients do? How does it change the graph of the parabola. What does a do, what does c do and a question still rarely asked, what does changing b do to change the graph. To see what b does more clearly we have you add a graph of the linear portion of the quadratic function to the picture so that you can see the pattern it makes and it causes the parabola to make. Quadratic functions give you a chance to really and experiment with this very important family of functions.