real, used in the 17th century by René Descartes, distinguishes realnumbers from imaginary numbers such as the square roots of −1. The realnumbers include
In mathematics, there are several equivalent ways of defining the realnumbers. One of them is that they form a complete ordered field that does not contain
property of the realnumbers that, intuitively, implies that there are no "gaps" (in Dedekind's terminology) or "missing points" in the real number line.
extends the realnumbers with a specific element denoted i, called the imaginary unit and satisfying the equation i 2 = − 1 {\displaystyle i^{2}=-1} ; every
rational numbers is usually denoted by boldface Q, or blackboard bold Q . {\displaystyle \mathbb {Q} .} A rational number is a real number. The real numbers