Here's the thing. You can take the advanced course first, and then take part A2. The result of this course is the sum of your two years. Of course, you can also take it directly together. Mathematics is divided into pure mathematics, advanced mathematics, etc. It is considered as an independent advanced course. In our school, AS takes all pure numbers and A2 takes all advanced numbers. In this way, we have two Alevel grades. Pure mathematics is relatively simple, and you will generally choose to take the exam, but high numbers are more difficult. You should choose whether to study or not according to your chosen major and personal inclination. I have never heard of core mathematics. Try to choose courses related to your major. Alevel also has many reward organizations. We are CIE, and each institution has a different examination syllabus and different teaching materials. So there will be all kinds of mechanics books, which should be selected according to the exams you take.