Sometimes the area or length is also d.

And the tolerance of arithmetic progression in the sequence is also D. ..

The domain is an unknown number, and the symbol of the range is (). The first one is a value that does not contain both sides. The second is inclusion, or they can be mixed.

Domain of definition

Definition domain refers to the range of independent variable X, which is one of the three elements of a function (definition domain, range and corresponding law) and the object of corresponding law. Finding the domain of function mainly includes three kinds of problems: abstract function, general function and function application.

Let X and Y be two variables, and the range of the variable X is D. If for each number x∈D, the variable Y always has a certain value corresponding to it according to a certain law, it is said that Y is a function of X, which is denoted as y=f(x), x∈D, X is called an independent variable, Y is called a dependent variable, and the number set D is called the domain of the function.