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Wiktionary
rational number

n. (context mathematics English) A number that can be expressed as the ratio of two integers.

WordNet
rational number

n. an integer or a fraction

Wikipedia
Rational number

In mathematics, a rational number is any number that can be expressed as the quotient or fractionp/q of two integers, a numeratorp and a non-zero denominatorq. Since q may be equal to 1, every integer is a rational number. The set of all rational numbers, often referred to as "the rationals", is usually denoted by a boldface Q (or blackboard bold Q, Unicode ℚ); it was thus denoted in 1895 by Giuseppe Peano after quoziente, Italian for " quotient".

The decimal expansion of a rational number always either terminates after a finite number of digits or begins to repeat the same finite sequence of digits over and over. Moreover, any repeating or terminating decimal represents a rational number. These statements hold true not just for base 10, but also for any other integer base (e.g. binary, hexadecimal).

A real number that is not rational is called irrational. Irrational numbers include , π, e, and φ. The decimal expansion of an irrational number continues without repeating. Since the set of rational numbers is countable, and the set of real numbers is uncountable, almost all real numbers are irrational.

The rational numbers can be formally defined as the equivalence classes of the quotient set where the cartesian product is the set of all ordered pairs (m,n) where m and n are integers, n is not 0 , and "~" is the equivalence relation defined by if, and only if,

In abstract algebra, the rational numbers together with certain operations of addition and multiplication form the archetypical field of characteristic zero. As such, it is characterized as having no proper subfield or, alternatively, being the field of fractions for the ring of integers. Finite extensions of Q are called algebraic number fields, and the algebraic closure of Q is the field of algebraic numbers.

In mathematical analysis, the rational numbers form a dense subset of the real numbers. The real numbers can be constructed from the rational numbers by completion, using Cauchy sequences, Dedekind cuts, or infinite decimals.

Zero divided by any other integer equals zero; therefore, zero is a rational number (but division by zero is undefined).

Usage examples of "rational number".

Then, because you sensed this was a rhetorical question in some way, you didn't try to explain first that there's no rational number for pi.

Just an ordinary little rational number, and then I met up with pi.