The main content of high school mathematics can be divided into two parts: "concept" and "problem". The "conceptual part" must have a clear and thorough understanding of the basic principles of mathematics, and then use mathematical concepts to solve problems. If your mathematical concept is very clear, no matter how the problem changes, you will be able to grasp the focus of the problem, and the "problem part" provides Some questions to test whether you really understand some of the concepts of mathematics.Therefore, for many years, the author often told the students the following important sentence:"Using mathematical concepts to solve problems and using problem solving to understand mathematical concepts"This book also uses the "concepts" and "problems" as the main structure of this book.