Interesting property of Op-Amp. It Inverts Transfer Function of the system in it's feedback
The classical feedback formula (H. Black) is

Ho=Ao/(1+AoH)=1/(1/Ao+H) with Ao=open-loop gain and H=feedback function.
Of course, for Ao approaching infinity we have Ho=1/H.

Example:
If the feedback path consists of a resistive voltage divider R1/(R1+R2) we get the classical closed-loop gain expression for a non-inverting opamp stage Acl=1+R2/R1.