Advanced mathematics is comprehensive and needs a strong sense of mathematics, such as finding triple integrals, strong spatial imagination, and thinking about two three-dimensional figures (such as the projection of the common volume of parabolic cylinder and spherical surface in three-dimensional coordinate system); Finding indefinite integral requires various deformations of the integrand function, which is a bit like this but more flexible than high school; The concept of multivariate function differentiation is abstract and easy to be confused. Infinite series needs differentiation or integration to calculate the required form, etc.