Centre of a group :
Let G be a group then centre of the group G is defined to be subset of all elements of G which commute with every element of G and it is denoted by Z(G). In symbols, Z (G )={a ∈G, ax= xa for all x in G
Results :
1. Z (G) is a subgroup of G.
2. G is abelian iff G= Z (G ).
3. Let G be a group and a ∈Z( G) then in the composition table of G the row and column headed by ‘a’ are same.
4. As zn and U (n) are abelian groups so they are centres of themselves i.e., z(zn)=zn and
Z(U(n))=U(n).
5 The Center of a group is ablian part of the group.
6 The Center of any group is non empty
7 The Center z(G) of a group G is a subgroup of G.
8 The Center of a group G is normal subgroup
9 The Center of a group is characteristics subgroup.
10 The Center of a group may not fully invariant subgroup.
11 The Center of an ablian group is the whole group and therefore cyclic group also.
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