The superposition theorem is used in circuits with multiple independent sources. To apply this theorem, keep one independent source at a time while replacing the inactive voltage source with a short-circuit and the inactive current source with an open-circuit, respectively. The theorem states that the voltage across or the current through an element in a linear circuit is the algebraic sum of the contributions from the independent sources. Consider a circuit with a voltage and a current source, where the voltage drop across a resistor must be determined. The voltage drop has contributions from both independent sources. The contribution of the voltage source is obtained by setting the current source to zero. By applying Kirchhoff's voltage law, the loop current is determined. Using Ohm's law, the voltage drop is calculated. Similarly, the current source contribution is obtained by setting the voltage source to zero. Combining the resistors, the equivalent resistance is obtained. Using the current division rule and Ohm's law, the voltage drop is determined. Finally, by adding the contributions from independent sources, the total voltage drop across the resistor is obtained.