Groups
Table of Contents
Part 1A Michaelmas
This is the first term of the Mathematical Tripos you should be taking this with the other first term courses at the same time as Cambridge designed it this way for a good reason.
Course
The point of studying groups is to learn a math framework for analyzing symmetry in complex structures like time series analysis. Books marked with † in the schedule are particularly well suited to the course and here that book is Algebra and Geometry by Alan F. Beardon which is on library genesis.
Additionally we have access to Modern Algebra which uses the text Visual Group Theory that is recommended by the schedule. A work book we can use which fills in some of the rigor left out by the VGT book is here and called An Inquiry-Based Approach to Abstract Algebra by Dana Ernst.
We have access to the first Cambridge lecture on Groups and the official lecture notes here from IA Groups (2019). Someone made complete lectures on YouTube based on the course notes too.
Cambridge lecture
I'm going to watch the Cambridge lecture on Groups first.
Modern Algebra
As stated above this course uses the Cambridge recommended book Visual Group Theory which you can get from libgen.is (library genesis has multiple domains if it doesn't work in your country) or Anna's Archive.