Graphing Quadratic Functions

I'll go a little faster about plotting quadratic graphs than about plotting linear graphs, because I assume that you already have some graphing experience.

Unlike linear graphs, graphs of quadratic functions are not straight and cannot be plotted with a ruler. But their form is always the same, they look like cow horns. The animal pictured here is a longhorn, not a cow, but the picture is too good to pass up.

The huge steel cable that supports San Francisco Bay's Golden Gate Bridge forms a parabola.

You are probably used to seeing the parabolas with the horns pointing up. But the graphs of quadratic functions with the coefficient for x² being negative, have horns pointing down.

• Identify the roots (if they exist) and plot them
• The midpoint of any parabola is the point x = -b/2a. Calculate the value of y in that point and plot it.
• Draw the coordinates so that the coordinate system includes the roots and the midpoint.
• Plot several points of the parabola, by calculating values of y for the values of x that you have chosen.
• Draw the line nicely