Question about a circuit to be solved with Norton's theorem

[link223]

Homework Statement

See picture please, it is highlighted in yellow.

Relevant Equations

Norton's theorem

Hello guys, I am new here.
I was wondering whether I could get some help about the highlighted part. What I don't understand is why we are able to ignore the 5-ohms resistor when we have short circuited terminals a-b.

Thanks in advance.

 

[Baluncore]

Welcome to PF.

What I don't understand is why we are able to ignore the 5-ohms resistor when we have short circuited terminals a-b.

Because a zero ohm resistor in parallel with a 5 ohm, (or any other resistor) is going to be zero ohms.

 

[link223]

Welcome to PF.

Because a zero ohm resistor in parallel with a 5 ohm, (or any other resistor) is going to be zero ohms.

Thanks! and thanks once again! I didn't think this through then.. makes total sense (also just noticed I was looking at fig(c) not (b) :'D) Thanks though!