To be fair, advanced mathematics is really a difficult course. If you are not a math major and just want to master the methods systematically, I suggest you study the textbooks and tutorials systematically:

Textbook: Advanced Mathematics (7th Edition) Volume I and Volume II.

Editor of Higher Education Press, Department of Applied Mathematics, Tongji University

Reference book: 1 Calculus Volume I and Volume II, edited by Department of Applied Mathematics, Tongji University, Higher Education Press.

2. Fundamentals of Engineering Mathematical Analysis, Volumes I and II, edited by Ma Zhien and Wang Miansen, Higher Education Press.

3. Mathematical Analysis Volume I and Volume II, edited by Chen of Fudan University, Higher Education Press.

4. Teaching Steering Committee of Higher Mathematics Problem Solving of Higher Education Press.

5. Examples and Exercises of Advanced Mathematics, edited by Tongji University Advanced Mathematics Teaching and Research Section, Tongji University Press.

If you want to systematically study the theoretical proof of higher mathematical theorems, it is recommended to study mathematical analysis. The teaching materials are suggested as follows: A Course of Mathematical Analysis by Shi Jihuai of the Chinese University of Science and Technology, followed by New Lecture on Mathematical Analysis by Peking University, Mathematical Analysis by Mei Qiang of Nanda University, and Mathematical Analysis by Zhou Minqiang and Fang of Peking University.

Please adopt!