In the WeChat service dy/dx, dy and dx can be separated, so there is dy/dx*dx/dy= 1, but what about the partial derivative? y/？ X is a whole and inseparable. This is related to the properties of multivariate functions. Multidimensional Euclidean space can not be regarded as one dimension, otherwise it will lead to operational errors.

Basic introduction

The driving force of overall development comes from the demand in practical application. In practice, some unknowns can sometimes be roughly estimated, but with the development of science and technology, it is often necessary to know the exact values. If the area or volume of simple geometry is needed, the known formula can be applied. For example, the volume of a rectangular swimming pool can be calculated by length x width x height. But if the swimming pool is oval, parabolic or more irregular, it is necessary to calculate the volume by integral.