# length

The length of a line segment is the distance between its endpoints. Length may be measured in meters, yards, abstract units, etc. For example, in the following diagram

$AB$ is one unit long, $BC$ is two units long, $CD$ is a fifth of a unit, $DE$ is four fifths of a unit, $AC$ is three units, etc.

The concept of length as defined above is a special case of a general concept called measure.

In two-dimensional space, length usually goes along the $x$ axis while height goes along the $y$ axis. The same holds in three-dimensional space.

For triangles, pentagons, and higher $n$-gons (http://planetmath.org/BasicPolygon), it is customary to refer to the length of any of its sides as the length of the . The length of a circle’s side is called its circumference.

In set theory, length refers to the number of elements a set (or one-dimensional array) has. This is also known as cardinality. For example, $\{2,5,11,23,47\}$ has length $5$.

 Title length Canonical name Length Date of creation 2013-03-22 16:31:45 Last modified on 2013-03-22 16:31:45 Owner PrimeFan (13766) Last modified by PrimeFan (13766) Numerical id 17 Author PrimeFan (13766) Entry type Definition Classification msc 51D20 Classification msc 51-00 Classification msc 51M25 Related topic Area2 Related topic Volume2 Related topic BasicPolygon Defines length of a polygon Defines length of a set