Preparations -- execute all comands in this section!

The display command -- used to overlay plots -- and other special plots
require that the plots-package be loaded first. (Other packages that are
handy in undergraduate math classes are linalg and student, also loaded
using the command with(packagename);

> with(plots):

Since angles are frequently of importance we set the global plot-preference
to draw all plots with equal scales along the axes.

> setoptions(scaling=constrained);

>