try functions.wolfram.com, eric weinstein's website, and other documentation
the localmachine Help no longer contains the methods used like it used to
sometimes lack of stating methods is because their is an actual patent on the method or it is confidential; for competitive reasons. but many not mentioned are not mentioned simply to keep the unweildy size of Help from overgrowing itself
if your book shows a method then likely mathematica's method is not wholey different. if there is "deficiency" in how mathematica calculates something - that's something that is normally mentioned in the documentation