low frequency response of transistors

Im having trouble understanding how to determine the 'R' that you have to exactly apply when using the formula f = 1/(2(pi)(R)(C)). For instance look at this screenshot from a page of "Electronic Devices and Circuit Theory" by R. Boylestad.

It says:
For the network of Fig. 11.16, the ac equivalent as “seen” by CE appears in Fig. 11.22.
The value of Re is therefore determined by
Re = RE|| ((R's/beta) + re), where R's = R1||R2||Rs
He just says the formula but he never says how he determined the formula to use. This is a big problem for me since there are problems in the book that have you analyze the low freq response of BJT and FET amplifiers which are of different configurations from the examples given in the discussion. Because the examples shown in the book are that of a voltage divider for BJT and a Self-bias for FET but the problems im facing in the book and in school feature fixed bias, collector feedback, common base, emitter follower, etc..
Basically, so what if i will deal with other circuit configurations, how do i determine what constitutes the 'R' in the above formula for frequency?
I'm trying to study by myself and not depend on the teacher but this is killing me
EDIT: In the rules of rewriting an amplifier circuit into its ac equivalent, you are supposed to short out capacitors but here in the above page Fig.11.22 is supposed to be the localized ac equivalent yet it has a capacitor.. why?

 

Let me flesh out my problem with this topic more specifically and in greater detail. Here are a bunch of things I don't get:

After you said that Harald I checked everything again and I realized that bypass and coupling capacitors are not negligible at low frequencies so they have to be present in the ac equivalent circuit, and the reason they are shorted when calculating for gain at midband frequencies is that their reactances are negligible for midband, and finally in highband frequencies they are still shorted for the same reason as in the midband but the interelectrode, wiring, and miller effect capacitances are beginning to affect your gain and therefore must not be neglected and will be present in your ac equivalent circuit.
So basically really small capacitances affect high frequency and large capacitances affect low frequency.

Despite knowing this, I am still unsure how to determine what constitutes R's in the formula f=1/(2(pi)RC) in the case when the emitter resistor is split into two parts: one part bypassed and one part unbypassed.
Here is a circuit that shows what i mean:

Here is my attempt to redraw this into an ac model(re approximation) at low frequency inputs, hence inclusion of the capacitors:

1.) So how do I determine the 'R' for solving the frequency filtered by the reactance of CE?
Normally if there is only one bypassed emitter resistor the R would be
R = RE||{[(R1||R2||RS)/BETA] + re} ...
2.) Also a problem point for me is I don't know what will constitute the 'R' in the frequency filtered by CS. Normally if there was only one bypassed emitter resistor the R would be
R = [R1||R2||(beta)*(re)] + RS, but with this kind of config would it change to
R = [R1||R2||(beta)*(re + RE1)] + RS ? *RE1 as in the part that isn't bypassed.

So how am I supposed to "look back" with this kind of configuration wherein the emitter resistor is split? How do i generate a formula? How do i deal with all situations?

For all I say below when I say gain i mean voltage gain and not current:
You know guys, I had my exams in this subject today and I'm pretty sure that I failed. We had 3 problems. The first was a common base amplifier and we have to solve for the midband gain and the upper and lower cutoff frequencies - I was totally screwed because I was assuming that the common base config wouldn't show up so I had no idea.. The second was an amplifier wherein we were given the bandwidth and the values of all the components and capacitances except for the wiring capacitance at the output, where we were supposed to determine how much wiring capacitance at the output would result in a bode plot exhibiting the given bandwidth. I think I knew how to solve it. The third was a two stage amplifier where we had to solve for the midband gain and the upper and lower cutoff frequencies, and I thought I had it down but i forgot to take into account the loading effect of the input impedance of the second stage to the voltage gain of the first stage as well as the effect of the load resistor to the gain of the second stage so pretty much all the calculations were wrong... It's hard not to be depressed with failing this subject when education is so expensive.

and dear moderators,
as this isn't exactly a homework assignment per se, maybe there doesn't have to be so much restriction to the help that people can give? it's too late anyway i already failed my exams..
And does anyone know any good resource material specifically for this, ones that are not vague and very enlightening? Do most electronics engineers really make amplifiers this way? or any advice you have to give me in general about this please it will be appreciated.

 

@ harald
Thank you very much. From first glances I like the link you gave me^. I will read it all.
As to searching through the internet, what I'm looking for is something that is very comprehensive yet accessible, which i must say is hard to find (that, or i suck at searching for things online) regarding this topic, even with the books in our library i have difficulty finding something that is comprehensive enough and with enough examples.. like a book electronics for idiots will get a 'check' for accessibility and examples but not comprehensiveness, while the book 'electronic devices and circuit theory' will get a 'check' for comprehensiveness but not accessibility in getting to the root of how to attack all the problems IMO..

 

Okay you just gave me an idea. I should simulate the different circuits using SPICE and then try to work out the formulae that matches the readings. thank you. I will update if it works. This way I'll be able to verify what exactly goes on.