Superposition: $$ \text{Voltage sources (short-circuit equivalent), Current sources (open-circuit equivalent)} $$
Thévenin’s Theorem: $$ R_{Th} \text{ all source to zero, } E_{Th} \text{ open-circuit terminal voltage} $$
Norton’s Theorem: $$ R_N \text{ all source to zero, } I_N \text{ short-circuit terminal current} $$
Maximum Power Transfer Theorem: $$ R_L = R_{Th} = R_N \text{ , } P_{max} = \frac{E_{Th}^2}{4R_{Th}} = \frac{I_N^2R_N}{4} $$