# Difference between revisions of "Centre (mathematics)"

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* In an algebraic structure, elements that commute with every element of the structure | * In an algebraic structure, elements that commute with every element of the structure | ||

** The [[centre of a group]], elements that commute with every group element | ** The [[centre of a group]], elements that commute with every group element | ||

+ | ** The [[centre of a ring]], elements that commute with every ring element | ||

* The centre of a [[Circle (mathematics)|circle]] | * The centre of a [[Circle (mathematics)|circle]] | ||

* The centre of mass, centroid or [[barycentre]] of a geometrical figure | * The centre of mass, centroid or [[barycentre]] of a geometrical figure |

## Revision as of 14:03, 22 December 2008

In mathematics, **centre** may refer to:

- In an algebraic structure, elements that commute with every element of the structure
- The centre of a group, elements that commute with every group element
- The centre of a ring, elements that commute with every ring element

- The centre of a circle
- The centre of mass, centroid or barycentre of a geometrical figure
- In triangle geometry
- The centroid, intersection of the medians
- The circumcentre, intersection of the perpendicular bisectors of the sides, centre of the circle through the vertices
- The nine-point centre
- The orthocentre, intersection of the altitudes
- The incentre, centre of a circle tangent to the sides
- The excentres, centres of the three circles internally tangent to one side and externally to the other two