Operational Amplifier (op-amp) part (1)

Reference:
Katsuhiko Ogata Modern Control Engineering 5th Edition
About op-amp :
An Operational Amplifier or op-amp is a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. It is a high-gain electronic voltage amplifier with a differential input and usually a single-ended output