How do I find v3 in this circuit?

Question

I'm going through this EMG circuit lab for practice (https://my.ece.utah.edu/~ece2240/ECE2240_Lab1b.pdf) but I'm stuck on the following calculations on pages 8-9.

1) Use the circuit model in Fig. 9(a) and the voltage-divider formula to find voltage drop v+ across R4.

2) Use the circuit model in Fig. 9(b) and Kirchhoff's and Ohm's law to find voltage drop v– across R2 and v3. In other words, v– is the sum of the voltage drops across R2 and v3.

3) Skip

4) Set v+ = v– and solve for v3 in terms of v1 and v2.

I know #1 should be v+ = (v2*R4)/(R3+R4). Is #2 just v- = v(R2) + v3? Shouldn't there be a v1 in there somewhere? How do I go about getting that? Thank you.

Answer 1

Yes, v- = v(R2) + v3 is correct in #2. You can get v(R2) by noting that v(R2) = i * R2, where i = (v1 - v3) / (R1 + R2).