Centre (mathematics)

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