We're going to sum the currents into node 1.

So, the first current is the current through R1 is going to be equal

to the voltage on one side of the resistor minus that on the other

divided by the resistor value.

So, it's going to be V1 minus V

minus divided by R1 and we know what V minus is.

It's the terms of V sub 2.

And so if we sum the second current through the feedback resistor R sub 2,

it's going to be V out minus V sub minus divided by R2.

That's going to be plus V out minus V minus divided by R2.

And our third current is the current that is flowing out of

the op amp back into that node 1.

And we know that value is 0.

I'm going to write it in, but It's one of our basic

characteristics of op amps that we want to make sure that we understand.