Limited to here, we must look at several points in the textbook, and never use high school textbooks or high numbers. Of course, it will be very painful to learn limit at first, and all theorems and proof ideas must be mastered, because even multivariate calculus has the same basic ideas, so this is the most basic. After laying the foundation of limit, it will be easier to learn calculus. If you are univariate, differential and derivative can be understood as one thing. After learning unary calculus and series, you still have to learn. If you learn line generation only at the level of Grade One, you'd better look at solving the equation first to know how to solve it, and then look at line generation directly, because you mainly focus on matrix and polynomial theory, which is not involved in middle school, but you'd better look at high generation rather than line generation, which is only a branch of high generation and has too little content. Spatial analytic geometry does not need to master too many things, just very basic. Finally, probability theory and statistics, probability that is not a high number can not be learned. If there is a higher need to learn advanced probability theory, you must throw away higher numbers, learn a few points directly, and then analyze them, then you can learn advanced probability theory, otherwise you can't understand things involving measurement and L P space.