<Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations. (April 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations. (April 2016) (Learn how and when to remove this template message) </Td> </Tr> <P> In mathematics, a real number is a value of a continuous quantity that can represent a distance along a line . The adjective real in this context was introduced in the 17th century by René Descartes, who distinguished between real and imaginary roots of polynomials . The real numbers include all the rational numbers, such as the integer − 5 and the fraction 4 / 3, and all the irrational numbers, such as √ 2 (1.41421356..., the square root of 2, an irrational algebraic number). Included within the irrationals are the transcendental numbers, such as π (3.14159265 ...). In addition to measuring distance, real numbers can be used to measure quantities such as time, mass, energy, velocity, and many more . </P> <P> Real numbers can be thought of as points on an infinitely long line called the number line or real line, where the points corresponding to integers are equally spaced . Any real number can be determined by a possibly infinite decimal representation, such as that of 8.632, where each consecutive digit is measured in units one tenth the size of the previous one . The real line can be thought of as a part of the complex plane, and complex numbers include real numbers . </P>

Square root of 9 belongs to what family of real numbers