how to tell which one is the entrance and which one is the exit of the feedback circuit?

 

Welcome to AAC

I don't see any feedback circuit? Did you forget to post a schematic?

 

here's the circuit, sorry, i forgot to post it.

 

So, as the name suggests, it "feeds back" a sample of the system output to the system input to modify, in some way, the transfer function. The input to the feedback circuit, therefore, is the system output or some relationship to it.

 

View attachment 294371
here's the circuit, sorry, i forgot to post it.

That's not a circuit diagram, post a real circuit so we can show you.

 

In your block diagram, the two conductors on the left side into A are the inputs and the two conductors out of A are the two connects to the right of A are the outputs.

Where did you get that image?

 

Understand that the output end of a feedback loop always sums with the input signal. and the input end of a feedback loop never connects with the input signal. That is applicableto the block diagram as well as to any detailed circuit drawing.

 

So the input is on the left and the output is on the right.