Hey mate, is this the one you pointing out?
Theory
Operational Amplifiers
Operational Amplifiers (OAs) are highly stable, high gain dc difference amplifiers. Since there is no capacitive coupling between their various amplifying stages, they can handle signals from zero frequency (dc signals)...
It looks it's complicated equation mate. I will try to show that equation to my mathematician classmate and try to understand it for you. Keep in touch mate.