*x*, written |

*x*| may be defined in a variety of ways. On a real number line, the absolute value of a number is the distance, disregarding direction, that the number is from zero. This definition establishes the fact that the absolute value of a number must always be nonnegative—that is, |

*x*|≥0.

A common algebraic definition of absolute value is often stated in three parts, as follows:

Another definition that is sometimes applied to calculus problems is

or the principal square root of *x* ^{2}. Each of these definitions also implies that the absolute value of a number must be a nonnegative.