I've got a problem because I don't understand the feedback factor in Op Amp.

All I know is that it is equal V-/Vout for negative feedback.

But what if V- is equal 0V ? Like here :

Also I heard that feedback factor is the reverse of the closed loop gain A = 1/B.

So is it -R1/R2 ? I've seen on some sites that it is R1/(R1+R2). I've even talked with some people and they say the same that feedback factor is equal -R1/R2.

And I'm confused but even if feedback factor is equal -R1/R2 or R1/(R1+R2). They how is it possible that it is equal 0V? I mean V-/Vout = B ("B" is for feedback factor). So 0V/Vout = B => 0V = B*Vout. It doesn't make any sense.