Deriving current expression from the info given

[noobish]

Homework Statement

I am doing some research and reading this: http://www.csuohio.edu/ece/theses/2004/Bhavin.pdf

I don't understand how the equation 4.1.11 on page 67 is derived.
Can anyone help clarify?

Homework Equations

(As in the pdf file)

The Attempt at a Solution

I have tried to understand it, but couldnt.

 

[merryjman]

It might be because this expression was not derived from the equations mentioned; in fact there IS no 4.2.3 at all, and 4.2.2 has nothing to do with 4.1.11. It appears this came from 4.1.8 and 4.1.9, where the expression for T(s) is substituted into 4.1.8 which is then solved for I(s). 4.1.11 factors out the omega(s) term and replaces the two j terms with one J term.