Calculate the output voltage if R₁ = R₂ = R₃ = 50 Ω, Rf = 1 kΩ, and V₁ = V₂ = V₃ = 50 mV.

Given: R1 = R2 = R3 = 50 Ω, Rf = 1 kΩ, and V1 = V2 = V3 = 50 mV

Due to virtual ground concept:

V_A = VB = 0  ----(1)

Apply Nodal analysis at Node 'A'

\(\frac{V_A-V_1}{R_1}+\frac{V_A-V_2}{R_2}+\frac{V_A-V_3}{R_3}+\frac{V_A-V_O}{R_f}=0\)

\(\frac{V_A-50\ mV}{50}+\frac{V_A-50\ mV}{50}+\frac{V_A-50\ mV}{50}+\frac{V_A-V_O}{1000}=0\)

\(\frac{3V_A}{50} +\frac{V_A}{1000}-3\ mV=\frac{V_O}{1000}\)

From equation 1);

\(-3\ mV=\frac{V_O}{1000}\)

V₀ = -3.0 V