Eulerian path puzzles

Problem:

Can you trace each of the following figures without lifting your pencil? No part of the figure, except for the intersection points, should be traced more than once.


Solution:

The first and second figures are traceable. The last figure is not.

One solution for the first figure is ABCDEBFGHIJKLMFLENCJHDAN.

One solution for the second figure is ABCDEFGBHAGIDJCIEJHFA.

The last figure is not traceable, as there are more than two vertices having an odd number of edges. In fact, there are four such vertices.


Sources: The Inquisitive Problem Solver