Hey,

For the attached question, the only part I do not understand is why the Thevenin Resistance is equal to R3.

I thought it would be (R1 || R2) + R3

Can somebody please explain this?

cheers!

 

The answer lies in the intrinsic impedances associated an ideal voltage source and an ideal current source.

See if you can find a statement in your textbook regarding the impedance of an ideal current source and the impedance of an ideal voltage source.

Armed with these two pieces of information, the answer to your question should become clear.

hgmjr