# Am I doing this ideal op-amp problem correctly?

**1. The problem statement, all variables and given/known data**

Consider the op-amp circuit at right: Assuming ideal op-amp behavior, compute v0 as a function of v1, v2, and v3

**2. Relevant equations**

Vp=Vn

Ip=In=0

**3. The attempt at a solution**

By voltage division:

Vp = 8/(8+8) V3

Vp = 1/2V3

Vn = 1/2V3

By node-voltage method at the inverting input terminal:

(Vn-V1)/4 + (Vn-V2)/4 + (Vn- V0)/8 = 0

Multiply equation by 8

2(Vn-V1) + 2(Vn-V2) + Vn-V0 = 0

V0 = Vn+2Vn-2V1+2Vn-2V2

V0 = 5Vn-2V1-2V2

Substitute in 1/2V3 for Vn

V0 = 5/2V3-2V1-2V2

Is this the correct answer? I’m pretty sure about the V1 and V2 part, because it matches the summing amplifier circuit equation of -(Rf/R1*V1+Rf/R2*V2). However, for V3, I don’t see how its resistor composition would yield an answer of 5/2. Could someone clarify?

Thanks

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