I have done many contest questions myself. The simplicity of elite mathematics has two aspects. 1. All problems in a broad vision are inseparable from books. They are just theorems in books, extensions of concepts added by teachers. There are no out-of-range problems. 2. The questions in the big field of vision are divided into plates. For example, in the third grade, there are special exercises for fillet and tangent. In this case, the idea is obviously simple. The classic topic of the Olympic Games is the Olympic Games. In addition to books, there are some theorems that are hardly used at ordinary times, such as Stewart theorem and Ptolemy theorem, which require students to have a wide range of knowledge and flexible ideas for solving problems. For example, many common knowledge points in a circle include vertical diameter theorem, tangent length theorem, circumferential angle theorem, secant theorem, chord truncation theorem and Ptolemy theorem, which are even less common.