Contemporary Abstract Algebra SEVENTH EDITION Joseph A. Gallian
Chapter 1: Introduction to Groups Symmetries of a Square The Dihedral Groups
1.1 Symmetries of a Square
The Square 1/3
The Square 2/3
The Square 3/3
Multiplication
The Dihedral Group The analysis carried out above for a square can similarly be done for an equilateral triangle or regular pentagon or, indeed, any regular n-gon (n ≥ 3). The corresponding group is denoted by and is called the dihedral group of order 2n.
The Dihedral Group This group has 2n elements n rotations, namely n reflection: Example: