D: meaningless, which can be understood as differential symbol followed by differential variable. For example, d (x 2) represents the differential of the function x 2.

Dx: First of all, it can be understood as the differential of variable X; Second, because X is usually used as an independent variable, it can also be understood as the differential of the independent variable X (that is, the differential component of the X axis).

D/dx: meaningless, which can be understood as the derivative of a function to the variable X (also called WeChat quotient, which is the quotient of differential), followed by the differential function. For example, (D/DX) (X 2) represents the derivative of the function X 2 to the variable X.

Dy/dx: it means the derivative of function y about x about independent variable x, and it can also be expressed as y, which will not cause confusion.