I can't get to understand how they simplify the positive feedback network of this op-amp. Can someone please give me hints or help me by explaining. Thanks very much.

 

Frankly speaking I don't see any simplification in this circuit.
The only thing that I can see is the error in Vi and Vo notation.

 

This is an RC oscillator. I got the question from my textbook. In the solutions manual they simplify the positive feedback network to that other circuit which is below the op-amp circuit. I don't understand how they do get that circuit.

 

This is an RC oscillator. I got the question from my textbook. In the solutions manual they simplify the positive feedback network to that other circuit which is below the op-amp circuit. I don't understand how they do get that circuit.

It is the same circuit.

The only reason Vo and Vi are flipped around is because the circuit that is not circled in red is from a "feedback perspective".

The output acts as the input for feedback, and this gets fed back to the input which is thought of output for the feedback circuit.

Got it?

 

It is the same circuit.

The only reason Vo and Vi are flipped around is because the circuit that is not circled in red is from a "feedback perspective".

The output acts as the input for feedback, and this gets fed back to the input which is thought of output for the feedback circuit.

Got it?

I get it now. Thanks man. This had me scratching my had big time. Now l will give another attempt to the question.