Real number is a general term for rational number and irrational number. Mathematically, a real number is defined as the number corresponding to a point 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 * * * together form 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.

Extended data

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.

Four algorithms of imaginary number:

(a+bi) (c+di)=(a c)+(b d)i

(a+bi)(c+di)=(ac-bd)+(ad+bc)i

(a+bi)/(c+di)=(ac+bd)/(c？ +d？ )+(bc-ad)i/(c？ +d？ )

Baidu Encyclopedia-Real Numbers