I recommend reading Ancient and Modern Mathematical Thoughts, written by an American, which is a big book. If you like math, you will be attracted and shocked by this book. You can see the content from the title, haha. You can see all kinds of mathematical thinking through the ages. The author is engaged in mathematics teaching, so his writing is very suitable for students. If you are a freshman in high school, you can read the first and third volumes directly without looking at the high numbers at the back. The first volume is similar to history, and the third volume is the mathematical thought summarized by the author. It is worthy of in-depth and meticulous reading.

There is also a book written by the Soviets, Content, Method and Significance of Mathematics, which talks about the thinking methods of different branches of mathematics. You can see what you have learned so far. It is also a book that is easy to understand, but it is worth understanding.

These two books are systematic and can help you to establish a general mathematical concept. It is also a well-known mathematical masterpiece, which will not let you go astray. There are many kinds of popular math books on the market, but most of them are business books. If you are interested in mathematics, I strongly recommend these two books. Come on!