Thevenin's Theorem:

Thevenin's theorem states that any linear electrical network containing independent and dependent sources and resistors can be replaced by an equivalent circuit consisting of a single voltage source (Thevenin voltage) in series with a single resistor (Thevenin resistance). This equivalent circuit accurately represents the behavior of the original network when viewed from the terminals where the load is connected

.Norton's Theorem:

Norton's theorem is similar to Thevenin's theorem but focuses on current sources instead of voltage sources. It states that any linear electrical network can be replaced by an equivalent circuit consisting of a current source (Norton current) in parallel with a resistor (Norton resistance) when viewed from the terminals where the load is connected

The maximum power transfer theorem states that maximum power is transferred from a source to a load when the load resistance is equal to the complex conjugate of the source impedance. This theorem is applicable when the objective is to maximize the power delivered to the load.