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## Homework Statement

Find the Thevenin equivalent at terminals a-b in the circuit below.

http://img361.imageshack.us/img361/2250/chapter5problem36gq0.jpg [Broken]

## Homework Equations

KVL, KCL, v = i R, current and voltage equations for Operation Amplifier

## The Attempt at a Solution

So I altered the diagram a bit.

http://img258.imageshack.us/img258/4382/chapter5problem36part2pr4.jpg [Broken]

[tex]I_1\,=\,\frac{V_S}{R_1}[/tex]

[tex]I_2\,=\,\frac{V_S\,-\,V_1}{R_2}[/tex]

KCL at [itex]V_S[/itex])

[tex]I_1\,=\,-I_2\,\,\longrightarrow\,\,\frac{V_S}{R_1}\,=\,-\frac{V_S\,-\,V_1}{R_2}[/tex]

[tex]V_1\,=\,\frac{R_2\,V_S}{R_1}\,+\,V_S[/tex]

[tex]V_{Th}\,=\,V_1\,=\,\frac{R_2\,V_S}{R_1}\,+\,V_S[/tex]

Is that right? If so, I will now put a test current of 1 Amp at the terminals to get the [itex]R_{Th}[/itex].

[tex]I_2\,=\,1[/tex]

[tex]\frac{V_S\,-\,V_1}{R_2}\,=\,1\,\,\longrightarrow\,\,V_1\,=\,V_S\,-\,R_2[/tex]

Now, using v = i R to get the Thevenin equivalent resistance.

[tex]R_{Th}\,=\,\frac{V_1}{1}\,=\,V_S\,-\,R_2[/tex]

Does that seem correct?

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