Copyright law governs the right to make copies and "derivative works" of original works. Making an unauthorized image of pages from a copyrighted book would be a violation.
However copyright law does not protect the underlying ideas from "copying". You are allowed to express the ideas of a copyrighted work in your own words (or mathematical formulas).
I'm not a lawyer, but we do have an obligation to understand and follow the law. So my advice is offered as a colleague/community member. Providing a link to Google books is okay, but the pages may not be visible in some countries precisely because the copyright law outside the US pretty uniformly lacks a "fair use" exemption for reproducing small amounts of a copyrighted work for a non-commercial purpose (I'm condensing a complex legal doctrine here).
As an international resource StackExchange in general (and Math.SE in particular) should be conservative with respect to asserting any "fair use" justification for image copying. Accordingly I think arbautjc should remove the images until time is found to restate the idea of the function "in your own words", leaving for now only a link to Google books or some other resource on the web, such as a legitimately posted paper or class note.
Faculty pages and arXiv.org are often good places to find such resources.