# Symmetry Group of Regular Hexagon/Examples

## Contents

- 1 Examples of Operations on Symmetry Group of Regular Hexagon
- 1.1 Subgroup of Operations that Fix $C$
- 1.2 Subgroup of Operations that Permute $A$, $C$ and $E$
- 1.3 Subgroup of Operations Generated by $\alpha^4$ and $\alpha^3 \beta$
- 1.4 Elements of Form $\beta \alpha^k$ in Form $\alpha^i \beta^j$
- 1.5 Center
- 1.6 Normalizer of $\alpha$
- 1.7 Normalizer of $\beta$
- 1.8 Normalizer of $\gen \alpha$

## Examples of Operations on Symmetry Group of Regular Hexagon

Let $\HH = ABCDEF$ be a regular hexagon.

Let $D_6$ denote the symmetry group of $\HH$.

Let $e$ denote the identity mapping

Let $\alpha$ denote rotation of $\HH$ anticlockwise through $\dfrac \pi 3$ radians ($60 \degrees$)

Let $\beta$ denote reflection of $\HH$ in the $AD$ axis.

### Subgroup of Operations that Fix $C$

The operations of $D_6$ that fix vertex $C$ form a subgroup of $D_6$ which is isomorphic to the parity group.

### Subgroup of Operations that Permute $A$, $C$ and $E$

The set of elements of $D_6$ which permute vertices $A$, $C$ and $E$ form a subgroup of $D_6$ which is isomorphic to the dihedral group $D_3$.

### Subgroup of Operations Generated by $\alpha^4$ and $\alpha^3 \beta$

Let $H$ be the subgroup of $D_6$ generated by $\alpha^4$ and $\alpha^3 \beta$.

Then:

- $H = \set {e, \alpha^2, \alpha^4, \alpha \beta, \alpha^3 \beta, \alpha^5 \beta}$

and:

- $H \cong D_3$

### Elements of Form $\beta \alpha^k$ in Form $\alpha^i \beta^j$

Consider elements of $D_6$ of the form $\beta \alpha^k$, for $k \in \Z^{\ge 0}$.

They can be expressed in the form:

- $\beta \alpha^k = \alpha^{6 - k} \beta$

### Center

The center of $D_6$ is:

- $\map Z {D_6} = \set {e, \alpha^3}$

### Normalizer of $\alpha$

The normalizer of $\alpha$ is:

- $\map {N_{D_6} } {\set \alpha} = \set {e, \alpha, \alpha^2, \alpha^3, \alpha^4, \alpha^5}$

### Normalizer of $\beta$

The normalizer of $\alpha$ is:

- $\map {N_{D_6} } {\set \beta} = \set {e, \beta, \alpha^3, \alpha^3 \beta}$

### Normalizer of $\gen \alpha$

Let $\gen \alpha$ denote the subgroup generated by $\alpha$.

The normalizer of $\gen \alpha$ is $D_6$ itself:

- $\map {N_{D_6} } {\gen \alpha} = D_6$