1) Thévenin's theorem states that a linear two-terminal circuit can be replaced by an equivalent circuit consisting of an ideal voltage source (VTh) in series with a resistor (RTh). 2) VTh is equal to the open-circuit voltage measured at the terminals. RTh is the equivalent input resistance measured when independent sources in the circuit are turned off. 3) To determine the Thévenin equivalent circuit, the load is replaced with an open circuit to find VTh, and then the sources are turned off to find RTh by measuring the resistance between the terminals.