Find the input resistance for the given circuit
(a) RIF = Ri*[1+(A*R4+R5)/(2* R4+R5)].
(b) RIF = Ri*[1+(A*R4)/(2* R4+R5)].
(c) RIF = Ri*[1+(A*R4+R5)/(R4+R5)].
(d) None of the mentioned
I have been asked this question in a dream while sleeping
This is a very interesting question from Differential Amplifiers with Multiple Op-Amp in section Operational Amplifier Characteristics of Linear Integrated Circuits