## Foundations of Mathematics## Set Theory |

## What is an ordered pair? |

An ordered pair is two quantities—usually written as (*a*, *b*)—that have a significant order; thus, (*a, b*) does not equal *(b, a).* Ordered pairs are used in set theory to define members in a function.

Ordered pairs are also valuable in linear equations and graphing, in which the *x* coordinate is the first number and the *y* coordinate is the second number, or (*x*, *y*). They are used on a grid to locate a point. (For more information about ordered pairs and graphs, see “Geometry and Trigonometry.”)