frequency response

I am studying RF circuit. I read the book "Elsevier - Telecommunication Circuits & Technology - 2000".The page image is attached. I know f= 1/2*pi*(Ro//RL) C where Ro is output resistance of transistor and RL is load resistor . I try to solve for equation(1.3) , I still cannot get that answer. Can anyone help me or hint me to do .thanks.

Correct approximated calculation is attached.But I still want detail calculation . for R3/R
If I was wrong , correct me.
thanks.