And, I want to know how it's cut-off frequency is derived.

Thanks for your help.

An LC low-pass filter:

http://www.williamson-labs.com/images/filters-lc.gif

(The first one, the Ui(jw) is at left for input and Uo(jw)) is the output at right.)

The first circuit.

What is the expression for G(jw) = Uo(jw) / Ui(jw)?

And What is the cut-off frequency wc?

{the value wc makes G(jwc) = 1/sqrt(2) * G(j0) }