The distance between the objective and the eyepiece of a simple
astronomical telescope is 80 cm.  The eyepiece is labeled "5x"
What is the angular magnification of the telescope?

The file lens_rays.pdf in this directory contains two diagrams:
a converging lens (f=+5) with object and a diverging lens (f=-5) with object.
Print out this file and then accurately (using a ruler) draw in the
three principal rays for each case.  Show where the image forms.
Calculate the image location and magnification and compare to what 
your drawing shows.