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I am having trouble understanding the difference between these two concepts. I know that input resistance is the resistance looking into the input terminals and output is looking into the output terminals. What I don't understand is how to evaluate these. In the image below, are the input and output resistances simply the Thevenin resistances at the input and output terminals?

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  1. Disconnect the source. Calculate the equivalent resistance seen across the open terminal Vi. That's Ri.
  2. Disconnect the load, as well as short the voltage source (prefect voltage sources have zero resistance). Calculate the equivalent resistance seen across the open terminal Vo. That's Ro.
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