Chapter Nine**

I particularly like the fact that it first proposed the concept of positive and negative numbers. This is a great progress in human understanding of numbers! Moreover, the "Insufficiency and Insufficiency Technique" is also very interesting. It is really smart to turn general equations into overs and deficiencies problems to solve. But I don't really like some of the math problems in it, they feel so difficult! But I will study hard. After all, this book has a major impact on the construction of human knowledge system, and I cannot miss it.