There are many concepts and formulas in postgraduate mathematics. In fact, following other teachers is not much different. I have listened to Tang Jiafeng's calculus foundation and intensive course before, and he has done two chapters 1800. I found that I didn't adapt to his teaching method. Later, I turned to Wu Zhongxiang. His basic skill is really conscientious, but at the same time, your pressure will be even greater. Wu Zhongxiang is more suitable for people with strong logical thinking ability. Tang Jiafeng's writing feels that his 1800 can be used as a workbook to brush the questions. In fact, both teachers speak very well, but they speak differently. Maybe your class suits him.
Something conclusive must be accumulated. As you said, the answer is different when you turn it over. Don't be too rigid in learning mathematics, and do more training for regular things; For special things, you should remember him; Remember what you don't understand and try to understand. Therefore, for those different problems, you will understand how he operates regularly, and you will practice it in practice; If it is irregular, you can only remember him, and he will appear on the test paper at some time.
The purpose of studying mathematics for postgraduate entrance examination is not to let you develop mathematical thinking, but to let you master the intention of the questioner and the commonly used examination methods and simply take the exam. This is my personal opinion. Some bosses can really get a leap in thinking in the process of studying mathematics in the postgraduate entrance examination, but for most people, they just want to be admitted to graduate school.