Real number

Rare card · No. 43305

In mathematics, a real number is a number that can be used to measure a continuous one-dimensional quantity such as a length, duration or temperature. Here, continuous means that pairs of values can have arbitrarily small differences. Every real number can be almost uniquely represented by an infinite decimal expansion. The real numbers are fundamental in calculus and in many other branches of mathematics, in particular by their role in the classical definitions of limits, continuity and derivatives. The set of real numbers, sometimes called "the reals", is usually notated as a bold R or the blackboard bold R {\displaystyle \mathbb {R} } . The adjective real, used in the 17th century by René Descartes, distinguishes real numbers from imaginary numbers such as the square roots of negative numbers. The real numbers include the rational numbers, such as the integer − 5 {\displaystyle...

Read on Wikipedia · Image User:Phrood~commonswiki, Public domain