Ξ

Xi in a capital letter Etymologicum Magnum (1499).

Xi (uppercase Ξ, lowercase ξ; Ancient Greek call ξ(ε) ῖ x(e)î /ksêː, ksîː/, in Modern Greek ξι xi /ksi/) is the fourteenth letter of the Greek alphabet, represents the sound [ks].

In the Greek numeral system it has a value of 60 (Ξʹ).

History

Epigraphic variants

In archaic epigraphic sources the following variants appear:

Use

An example of known use of this numeration is the Number of the Beast, in the Apocalypse of Saint John, where it appears as χξςʹ (ji, xi, stigma), representing the value 666.

In mathematics it can denote the roots of a system of equations, especially the unit roots (the complex roots of the polynomial Xⁿ - 1, where n is a natural number). In the general case, it usually has subscripts, while, in the case of unit roots, all of them can be expressed as powers of a primitive unit root ξ.

Also used in thermodynamics to denote the progress of a reaction, and in particle physics to denote the particle cascade.

In Wave Physics it represents the kinematic displacement of any particle within a traveling wave:

roga roga (x,t)=roga roga 0without (kx± ± ω ω t){displaystyle xi (x,t)=xi _{0}sin(kxpm omega t)}

Recently, in the field of geotechnics, researchers from the University of Cantabria adopted this letter to name the constant PECM, which relates the capacity per tip and capacity per shaft in a pile for a given material and soil profile..

It is also used as the symbol for Ethereum's cryptocurrency, Ether.

Unicode

• Greek and Coptic

• Maths