I tryed to use Cross multiplication and Conjugate roots to factor the transfer function of two-zero feed-forward filter but...I can‘t get the result like :

(1-Z1z^-1)(1-Z2z^-2) on p362.

The name of the book is Designing Audio Effect Plugins in C++

Same function can be found here but no explation about how to factor:https://ccrma.stanford.edu/~jos/filters/Two_Zero.html