in Q₂ increases, increasing V₂ and decreasing the difference V₁ - V₂ entering the op amp. Consequently, the base voltage of Q₂ is decreased, and V_BE of Q₂ decreases, counteracting the increase in output current.

If the op-amp gain A_v is large, only a very small difference V₁ - V₂ is sufficient to generate the needed base voltage V_B for Q₂, namely
:

Consequently, the currents in the two leg resistors

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