How can the formula be derived?

The formulas 5.12(a, b&c) in the book Microstrip Filters for RF/Microwave Application (Jia-Sheng Hong, Lancasterr) are likely derived from the equations in Figure 3.20. However I don't konw how to obtain the formulas 5.12 form the equations in Figrue 3.20 or other equation. Where does π/2 under the radical sign come from?
I hope someone can tell me how can the formulas 5.12 be obtained.

Thanks in advance

flywke

pls post the equations

no one knows what you are talking about without the book

Sorry for the absence of the formulas. I have pasted the formulas as an attachment.
The upper is the formula in Figure 3.20 and the lower is the formula 5.12.