In Chapter 8 Appendix of the Walsh book (page 379), he approximated equation (8.80). Who can provide me with the details of how to approximate the equation?
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Sorry, but do you expect users to find out which book and edition you are referring to, get a copy and then search for the answer? If you want people to help you, you need to make their life as easy as possible, provide all required information, and pose precise questions.