Variable

A variable is a mathematical symbol which is used to represent a member of a given set and is typically denoted by a letter such as x, y, or z. The idea of a variable, invented during the late sixteenth century, is characteristic of modern mathematics and was not widely used in ancient times. Since a variable reflects a quantity which can take on different values, its use has become a critical part of nearly all disciplines which use mathematical models to represent the real world.

The idea of using letters to represent variables was first suggested by the sixteenth century mathematician François Viète (1540-1603) in his work, In artem analyticam isagoge (1591). Although his notations barely resemble our modern day symbolism, they were an important step in the development of the concept of using a letter to represent a changing value in a mathematical equation. His ideas were further developed in the decades that followed. Rene Descartes (1596-1650) is generally credited for making standard, the use of the letters x, y, and z for variables.