Why is Thevenin resistance equal to R3, not (R1 || R2) + R3?

[vg19]

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!

 

[Isma]

lol i also think wat u think(dont count on that though my ckts suck)...do tell me too why it isnt:d

 

[SGT]

The second hand drawn figure shows it. R1 and R2 are not in parallel. They are in series and their series connection is in parallel with a short circuit, so the equivalent resistance of this connection is zero.