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real number

Any number that can be represented as a, possibly infinitely long and non-repeating, decimal. Real numbers stand in one-to-one correspondence with the points on a continuous line, known as the real number line, that stretches from zero to infinity in both directions. The set of real numbers contains the set of all rational numbers and the set of all irrational numbers. The name "real number" is a retronym, coined by René Descartes in response to the concept of imaginary numbers. Number systems that are even more general that the real numbers include the complex numbers and, of much more recent discovery, hyperreal numbers and surreal numbers.

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