Problem 1 Three β networks are shown along with the type of A amplifier if this is to be used in a standard feedback network. Determine the value of β in all three cases. You may assume the port impedances of the A amplifier are ideal and that the signal propagation through the β network is in the direction of the arrow. 
I have the first one as
Vr2=(R2/(R2+R3))Vi
Vo=(R1/(R2+R1))Vr2
Vo=(R1/(R2+R1))((R2/(R2+R3))Vi)
I have the second one as
Iout=(R3/(R3+R4))Iin
Vout=Iout*R3
Vout=(R3^2/(R3+R4))Iin
because it is transresistance meaning current in and voltage out
For the third one Im not sure how to solve this using Voltage in and Current outwith only one reistor there I know Vout=Vin so would Iout=Vin/R5?
