Thevenin’s Theorem

$v_t=v_{oc}$ $i_{sc}=\frac{v_{oc}}{R_t}$ $oc$ stands for “open circuit” $R_t=\frac{v_{oc}}{i_{sc}}$ $sc$ stands for “short circuit”

Any resistive linear circuit between two terminals is equivalent to an independent voltage source in series with a resistance.

Test Source

Add a test source when there is a dependent source. If the sources are independent, no need to introduce test source.

title: With dependent source
Recommend using a test source of $V=1$ or $I=1$ to make you calculations simpler. 

Related

• Norton’s Theorem