1, high-dimensional nonlinear problem: from the oldest three-body to the NS equation of fluid mechanics, and then to Einstein's general relativity equation, it involves a wide range, many exercises and is difficult;

2. Limit problem: the core content of calculus is limit, and the definition of limit is one of the most difficult contents of this course. The definition of limit is divided into the definition of sequence and the definition of function, which is difficult to understand because it involves many functions.

3. Function questions: including elementary function questions, medium function questions and advanced function questions, which cover a wide range, occupy a large proportion in the exam, and involve many difficult problems.