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The real numbers can be constructed as a completion of the rational numbers, in such a way that a sequence defined by a decimal or binary expansion like (3; 3.1; 3.14; 3.141; 3.1415; ...) converges to a unique real number—in this case π.
Any real number can be approximated to any desired degree of accuracy by rational numbers with finite decimal representations. Assume x ≥ 0 {\displaystyle x\geq 0} . Then for every integer n ≥ 1 {\displaystyle n\geq 1} there is a finite decimal r n = a 0 . a 1 a 2 ⋯ a n {\displaystyle r_{n}=a_{0}.a_{1}a_{2}\cdots a_{n}} such that:
That is, fractions of the form a/10 n, where a is an integer, and n is a non-negative integer. Decimal fractions also result from the addition of an integer and a fractional part; the resulting sum sometimes is called a fractional number. Decimals are commonly used to approximate real numbers.
Computable number: A real number whose digits can be computed by some algorithm. Period: A number which can be computed as the integral of some algebraic function over an algebraic domain. Definable number: A real number that can be defined uniquely using a first-order formula with one free variable in the language of set theory.
Other integer data types are implemented with a fixed size, usually a number of bits which is a power of 2 (4, 8, 16, etc.) or a memorable number of decimal digits (e.g., 9 or 10). Cardinality The set of integers is countably infinite , meaning it is possible to pair each integer with a unique natural number.
An axiomatic definition of the real numbers consists of defining them as the elements of a complete ordered field. [2] [3] [4] This means the following: The real numbers form a set, commonly denoted , containing two distinguished elements denoted 0 and 1, and on which are defined two binary operations and one binary relation; the operations are called addition and multiplication of real ...
The representation has a limited precision. For example, only 15 decimal digits can be represented with a 64-bit real. If a very small floating-point number is added to a large one, the result is just the large one. The small number was too small to even show up in 15 or 16 digits of resolution, and the computer effectively discards it.
Various features of repeating decimals extend to the representation of numbers in all other integer bases, not just base 10: Every real number can be represented as an integer part followed by a radix point (the generalization of a decimal point to non-decimal systems) followed by a finite or infinite number of digits. If the base is an integer ...