Who can help me think about the negative feedback in analog circuit?

In the voltage-current negative feedback,what is the value of the negative feedback voltage of the output voltage? It says that "Vref=3DVo*Re1/(Re1+Rf)" in the text book,why is that? Should I consider the output resistance of the emission pole of the first transistor?I think the Re1 should be taken place by Re1//(rbe/(=DF+1)),and there also should be an equivalent negative voltage that equals to be vi*rbe/(Re1*(=DF+1)). I think there may be something wrong with my consideration, who can help me? Is there any way to upload the schematic?=20 Thanks in advance!