An important note regarding the analysis of simple RC filters:
the f=1/(2πRC) equation solves for the frequency where R = XC (capacitive reactance).
So for a simple high or low pass RC filter, it would seem like the analysis would be the same as for a voltage divider where R1=R2. It is the same as far as power is concerned, but you will get an incorrect answer for voltage amplitude. For voltage, -3dB is about 70% voltage output. The reasoning here is that the voltage and current is out of phase. If only voltage matters (as in most signal processing) then the -3dB figure applies.
http://www.sengpielaudio.com/calculator-RC.htm
ω is the lowercase Greek letter Omega. It is the symbol for angular frequency.
ω = 2πf