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Commutative Diagram Line Segment Number Cardinality Metric Space Circle Set Theory Triangle Basic Polygon Unit Endpoint Measure On A Boolean Algebra Pentagon Central Collineations Height Of A Triangle

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Basic 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

$\begin{pspicture}(-1,-0.3)(13,0.3) \psline{<->}(-1,0)(13,0) \psdots(0,0)(3,0)(9,... ...){$D$} \rput[b](12,0.2){$E$} \rput[l](-1,0){.} \rput[r](13,0){.} \end{pspicture}$

is one unit long, is two units long, is a fifth of a unit, is four fifths of a unit, 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 axis while height goes along the axis. The same holds in three-dimensional space.

For triangles, pentagons, and higher -gons, it is customary to refer to the length of any of its sides as the length of the polygon. 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 .

1	Commutative Diagram
1	Circle
1	Triangle
1	Basic Polygon
1	Metric Space
1	Set Theory
1	Line Segment
1	Cardinality
1	Number
2	Unit
2	Endpoint
3	Measure On A Boolean Algebra
3	Central Collineations
3	Pentagon
4	Height Of A Triangle