For each cyclic groupthere is an element – not necessarily unique – that generates the group, so that every element of the group is a result of repeated composition of some element with itself. If
is such an element, and the group
has
elements, we can write
A group does not have to be cyclic to have a set of elements that generate the group. The group of symmetries of the rectangle is generated by the elementsand
reflections in the vertical and norizontal lines through the centre of the rectangle.
The group of symmetries isHoweve
and
so
is said to generate the group. Other choices are possible.
and
also generate the group.
Similary the group of symmetries of the equliateral triangle,is generated by the set
since
and
Other choices are possible.
and
also generate the group.
and
also obey the relationship
Knowing the generators of as group and the relationships between them allows us to simplify any expression involving the elements of the group.
For the groupabove, suppose we have the sequence of operation on the equilateral triangle
(1).
implies
so
(1) becomes
then implies
Finally,