Math d means differential. Two sets of numbers a and b are obtained from the function B=f(A). In A, when dx approaches itself, the limit of the function at dx is called the differential of the function at dx, and the central idea of the differential is infinite division. Differential is the linear main part of function change. One of the basic concepts of calculus.

The concept of differentiation is produced in solving the contradiction between straight and curved. In tiny parts, straight lines can be used instead of curves to approximate, and its direct application is the linearization of functions. Differential has a double meaning: it represents a tiny quantity, so the numerical calculation result of a linear function can be regarded as the numerical approximation of the original function, which is the basic idea of approximate calculation by differential method.