Equivalence Of Thevenin's And Norton's Theorems

According to Thevenin's theorem a two terminal power supply can be represented like this:

And According to Norton's theorem the same power supply can be represented like this:

From the Thevenin circuit we have

IL = VT/(Rint+RL)

From the Norton circuit we have

VAB = ISC(RintRL/(Rint+RL))
        = ILRL 
ILRL = ISC(RintRL/(Rint+RL))
IL = VAB/RL 
    = ISCRint/(Rint+RL)

V_AB is the same for both circuits, so we can substitute what we stated I_L was for the Thevenin circuit:

ISCRint/(Rint+RL) = VT/(Rint+RL)
ISCRint = VT

Both theorems give us a way to represent complicated circuits as simpler ones, either as a simple series circuit, or a simple parallel circuit.

References

Fischer-Cripps. A.C., The Electronics Companion. Institute of Physics, 2005.