Real number is a general term for rational number and irrational number. Mathematically, real numbers are defined as the number of corresponding points on the number axis. Real numbers can be intuitively regarded as one-to-one correspondence between finite decimals and infinite decimals, and between real numbers and points on the number axis. But the whole of real numbers can't be described only by enumeration. Real and imaginary numbers * * * make up a complex number.

Real numbers can be divided into rational and irrational numbers, or algebraic and transcendental numbers. Real number sets generally use black letters? r？ Express delivery. R stands for n-dimensional real number space. Real numbers are uncountable. Real number is the core research object of real number theory.

The set of all real numbers can be called real number system or real number continuum. Any complete Archimedean ordered field can be called a real number system. It is unique in the sense of order-preserving isomorphism, and is often expressed by R. Because R is an arithmetic system that defines arithmetic operations, it is called the real number system.

Real numbers can be used to measure continuous quantities. Theoretically, any real number can be expressed as an infinite decimal, and to the right of the decimal point is an infinite series (cyclic or acyclic). In practice, real numbers are often approximate to a finite decimal (n digits are reserved after the decimal point, and n is a positive integer). In the computer field, because computers can only store a limited number of decimal places, real numbers are often represented by floating-point numbers.

The basic operations that real numbers can realize are addition, subtraction, multiplication, division, multiplication and so on. For non-negative numbers (that is, positive numbers and 0), you can also perform a root operation. The result of addition, subtraction, multiplication, division (divisor is not zero) and square of real numbers is still real numbers. Any real number can be raised to an odd power, and the result is still a real number. Only non-negative real numbers can be raised to even powers, and the result is still real numbers.