Why Does the Current Halve at This Frequency in an AC Series Circuit?

[sma235]

Homework Statement

A series circuit contains only a resistor and an inductor. The voltage V of the generator is fixed. If R = 12 ohms and L = 4.5 mH, find the frequency at which the current is one-half its value at zero frequency. Note: The ac current and voltage are rms values and power is an average value unless indicated otherwise.

Homework Equations

f=sqrt(3R)/2*pi*L

The Attempt at a Solution

I calculated 212.21 Hz but this was incorrect

 

[ehild]

Your equation for the frequency is wrong. How did you get it? ehild