Analysis: Following the Th´ evenin equivalent resistance methodology box, we first set
the current source equal to zero, by replacing it with an open circuit, then set the voltage
source equal to zero by replacing it with a short circuit. The resulting circuit is depicted in
Figure 3.39. Looking into terminal a-b we recognize that, starting from the left (away
from the load) and moving to the right (toward the load), the equivalent resistance is given
by the expression