(Note: Like most rules, there are some exceptions to these opamp rules. We wouldn't have to go through the tedious rigamarole of solving a bunch of new equations for node voltages and mesh currents, because we wouldn't be disturbing either of them by adding a voltage follower. In practice, this has some pretty neat implications: if V+ isn't drawing any current, then it means that we could connect Vin to any node in any circuit and measure it without modifying the original circuit. This is really just a way of saying that V+ has a really high impedance - in fact, since we're talking about ideal opamps, we tend to just say that it has infinite input impedance. Looking at the first rule, we can see that our voltage follower circuit is not drawing any current at the input terminal connected to V+. This property is sometimes called the virtual short approximation.
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