Absolute value

The absolute value of a number may be thought of as its distance from zero.

Some additional useful properties are given below. These are either immediate consequences of the definition or implied by the four fundamental properties above.

These relations may be used to solve inequalities involving absolute values. For example:

For both real and complex numbers the absolute value function is idempotent (meaning that the absolute value of any absolute value is itself).

The absolute value function of a real number returns its value irrespective of its sign, whereas the sign (or signum) function returns a number's sign irrespective of its value. The following equations show the relationship between these two functions:

The real absolute value function is an example of a continuous function that achieves a global minimum where the derivative does not exist.

The antiderivative (indefinite integral) of the real absolute value function is

The absolute value is closely related to the idea of distance. As noted above, the absolute value of a real or complex number is the distance from that number to the origin, along the real number line, for real numbers, or in the complex plane, for complex numbers, and more generally, the absolute value of the difference of two real or complex numbers is the distance between them.

The above shows that the "absolute value"-distance, for real and complex numbers, agrees with the standard Euclidean distance, which they inherit as a result of considering them as one and two-dimensional Euclidean spaces, respectively.

The properties of the absolute value of the difference of two real or complex numbers: non-negativity, identity of indiscernibles, symmetry and the triangle inequality given above, can be seen to motivate the more general notion of a distance function as follows:

The four fundamental properties of the absolute value for real numbers can be used to generalise the notion of absolute value to an arbitrary field, as follows.

Again the fundamental properties of the absolute value for real numbers can be used, with a slight modification, to generalise the notion to an arbitrary vector space.