Q stands for the set of rational numbers: Q={ab∣a∈Z, b∈Nba∣a∈Z, b∈N}, and the q of the set of rational numbers is the first letter of English/German quotient, because all rational numbers can be written as the quotient of two integers, the real number R.

Q's representative:

Q stands for rational number set. The set of all positive integers is called positive integer set, which is denoted as N*, Z+ or n+; The set composed of all nonnegative integers is called nonnegative integer set (or natural number set), and is denoted as n; The set composed of all integers is called integer set, which is denoted as z; The set of all rational numbers is called rational number set, and it is denoted as Q.

The set composed of all real numbers is called real number set, which is denoted as r; The set composed of all imaginary numbers is called imaginary number set, which is denoted as I; The set of complex numbers composed of all real numbers and imaginary numbers is called complex number set, and it is recorded as C.

A rational number is a number that can be written as the ratio of two integers. Rational numbers include integers and fractions. A fraction is a rational number that is not an integer. All finite decimals and infinite cyclic decimals are fractions. Real number is a general term for rational number and irrational number. Irrational number is an infinite cycle decimal, which cannot be written as a real number of the ratio of two integers. All decimals and integers are real numbers.

Real number = {rational number} ∨ {irrational number} and complex number. Complex number refers to a+bi(a, b are real numbers, where I 2 =-1). Complex number is a general term for real number and imaginary number. Where b=0, complex numbers are real numbers, others are imaginary numbers, a=0, and b≠0 is pure imaginary numbers.

There is also a super real number, which is a set of numbers that expand infinite and infinite decimals in a real number set. Natural number: n, positive integer: N+, integer: z, rational number: q, real number: r, complex number: C. Natural number, positive integer, integer, rational number is countable set, real number and complex number are uncountable set.