Greetings, I want to tell me if i calculated well the following amplifications. I took several cases when the first stage is common emitter/base/collector connected to second stage with common emiiter/base/collector. Firsly i calculated the impedance of the stage 2 amplifier seen by the first amplifier and also i want to confirm me if my logic is good. When we connect the 2 amplifiers, each amplifier acts like an impedance for the other amplifier??? So, i calculated the impedance of the second stage seen by the first stage when the second stage is connected to the first stage with its emitter(RTA in photo), base(RTB in photo) and collector (RTC in photo). Then i took all posibilities i could imagine of connections and i calculated the voltage gain of the first amplifier and i noted on circuit the second amplifier with RTA, RTB and RTC. Im not sure on my work on calculating RTC, number 2 case when T1 is common base and the emitter is connected to the second stage. RT(A,B,C) means that the impedance could be RTA, RTB or RTC, any of these 3. Also i can have some sign mistakes on amplifications but ignore them. Another question. It seems like the impedance of the second amplifier seen by the first amplifier is always the input impedance of the second amplifier, its this somthing like a rule???