I highly recommend Peter Higgins’ Algebra: A Very Short Introduction (a title of the VSI-series published by OUP) as an excellent and accessible introduction (as the title says) to some of the major fields of advanced algebra. The brief but comprehensive 137-page volume eases you into the subject in its first few chapters by explaining in detail the fundamental laws and rules of arithmetic and demonstrating how more complex algebraic laws and theorems can be inferred from these axioms. Higgins thus provides a deeper insight into basic algebraic knowledge, showing the algebraic reasoning and proofs behind well-known theorems (Sätze) learnt in maths lessons at school.
In the following chapters, the author delves into linear and quadratic equations, illuminating, for example, how the famous quadratic formula to solve such equations was derived. After a challenging excursion into the subject area of polynomials and cubic equations, Peter Higgins next presents a succinct overview over the defining features of groups, rings and fields before moving on to the topic of modular or clock arithmetic which involves calculations based on equivalences between elements of least residue classes.
The last and most extensive section of the book is dedicated to linear algebra, a major field concerned with networks, matrices and linear (i.e. matrix) transformations of points in n-dimensional space. You will learn about matrix inverses, determinants and eigenvectors and -values, among other things.
In the last chapter Higgins briefly delves into the topics of vector spaces, which are fundamental to linear algebra, and of finite fields - these latter being central to cryptography and other areas of applied mathematics and also playing an important role in the famous proof of Fermat’s Last Theorem by Sir Andrew Wiles in the 1990s.
In summary, Algebra: A Very Short Introduction by Peter M. Higgins is a concise, rigorous and intellectually rewarding excursion into the (for non-academics) often unknown territories of advanced algebra. A must-read primer and excellent reference work for anyone interested in higher mathematics.