In a given transistor, the emitter current is changed by 2.1 mA. This results in a change of 2 mA in the collector current and a change of 1.05 V in the emitter-base voltage. The input resistance is:

5000 Ω 3000 Ω 1000 Ω 500 Ω

500 Ω

Input resistance = $\frac{ΔV_{EB}}{ΔI}=\frac{1.05}{2.1×10^{-3}}=500Ω$