According to my professor's model answer for an assignment, when we derive the transfer function of an op amp circuit, we have a "K" value, which is the open loop gain of the op amp (I am not 100% certain), multiplied to the op amp circuit (1+R1/R2 for non-inverting amplifier for example). I need to multiply the "open loop gain" with "close loop gain" in order to get the transfer function for a specific circuit. However, when I read the non-inverting amplifier section in "fundamental of microelectronics" by Ravazi, his explanation is in the following: "Interestingly, the voltage gain depends on only the ratio of the resistors; if R1 and R2 increase by 20%, R1/R2 remains constant." It's on page 358 for 2nd edition. I just wonder which version is correct.