In Chapter 3, page 3-31, at Eq 3.27, the second denominator is incorrect. What is rt extc? I had difficulty retrieving older versions of the book (links aren’t given for other versions than 3.0j), it could help to be able to download older revisions easily.
Problem in version 3.0j: http://www.cds.caltech.edu/~murray/books/AM08/pdf/fbs-modeling_08Aug2019.pdf
Different in version 3.0i : http://www.cds.caltech.edu/~murray/books/AM08/pdf/fbs-modeling_03Oct18.pdf (page 3-32, eq 3.27)