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The real numbers include the rational numbers, such as the integer −5 and the fraction 4 / 3. The rest of the real numbers are called irrational numbers. Some irrational numbers (as well as all the rationals) are the root of a polynomial with integer coefficients, such as the square root √2 = 1.414...; these are called algebraic numbers.
In fact, all square roots of natural numbers, other than of perfect squares, are irrational. [2] Like all real numbers, irrational numbers can be expressed in positional notation, notably as a decimal number. In the case of irrational numbers, the decimal expansion does not terminate, nor end with a repeating sequence.
These include infinite and infinitesimal numbers which possess certain properties of the real numbers. Surreal numbers : A number system that includes the hyperreal numbers as well as the ordinals. Fuzzy numbers : A generalization of the real numbers, in which each element is a connected set of possible values with weights.
A real number that is not rational is called irrational. [5] Irrational numbers include the square root of 2 ( ), π, e, and the golden ratio (φ). Since the set of rational numbers is countable, and the set of real numbers is uncountable, almost all real numbers are irrational. [1]
In mathematics, an irrational number is any real number that is not a rational number, i.e., one that cannot be written as a fraction a / b with a and b integers and b not zero. This is also known as being incommensurable, or without common measure. The irrational numbers are precisely those numbers whose expansion in any given base (decimal ...
Another well-known number, proven to be an irrational real number, is = …, the square root of 2, that is, the unique positive real number whose square is 2. Both these numbers have been approximated (by computer) to trillions ( 1 trillion = 10 12 = 1,000,000,000,000 ) of digits.
The decimal representation of an irrational number is infinite without repeating decimals. [23] The set of rational numbers together with the set of irrational numbers makes up the set of real numbers. The symbol of the real numbers is . [24] Even wider classes of numbers include complex numbers and quaternions. [25]
Other real numbers have decimal expansions that never repeat. These are precisely the irrational numbers, numbers that cannot be represented as a ratio of integers. Some well-known examples are: √ 2 = 1.41421356237309504880... e = 2.71828182845904523536...