Useful, but it is impossible to learn the formula of mathematical backrest well! The key is whether you can learn, such as doing more questions, what kind of questions? Of course, it is a college entrance examination question. Buy two sets of college entrance examination examples, summarize the same type of questions, and then read them again and again! As for how to summarize, I think as long as you are not a fool, you should know these things and how to use them, not finish the task! That's useless!