The first, accessible on every page header, is a Google-powered search on the text of the pages on this site. This means it searches the Mathematica input forms and text comments that are on the pages.

A typical search of this kind could contain the search string "Cos Sin Tan OR Cot -Sec", which would return all pages that contain the words "Cos" and "Sin", either "Tan" or "Cot", but not "Sec" anywhere.

The second, advanced search is a mathematical or content-based search. This search's criteria refer to the mathematical content of the identities, so this search can find elements that might not appear literally in a page, like E^x contains an exponential function but no textual occurrence of "Exp". This search can be accessed by clicking the "Formula Search" button, which appears in the top header of each page. More details are available about this search.