Bob your answer is correct but putting a 10K resistor in series with the input and feeding it with a 1V 1KHz sine will allow you to use simple ohms law. Measuring the voltage drop across the 10K to calculate the current flow, then subtract the voltage dropped across the 10K from the 1 volt input. Use R=V/I to calculate your input impedance, providing it is purely resistive. Good job Bob, I liked your answer too.
