Look at Part-66 Annex I
Why don't you simply look at the Appendix 1 to Part-66 and look at the knowledge requirements for Maths. This is the smallest unit compared to all the other units. It tells you exactly what you need to learn.
Get a good book, or even go online, and learn what you need. You should find the required knowledge in any good GCSE and A level maths book. The maths is not higher than A level, and even then, it's pushing it.
Part-66 annex 1 gives you pages and pages of all knowledge requirements for all Part-66 exams. This is a good guide to what you need to learn and know. You can tick off each bit of knowledge as you learn it (basic, medium or thorough as described in the annex).