# Exam Prep Help

• Apr 26th 2009, 05:38 PM
MrJack1990
Exam Prep Help
For the dihedral group($\displaystyle D_4 \mbox{or} \ D_8$) with $\displaystyle \sigma = \begin{pmatrix} 1&2&3&4\\2&3&4&1 \end{pmatrix} \ \mbox{and} \ \tau = \begin{pmatrix} 1&2&3&4\\2&1&4&3 \end{pmatrix} \mbox{and}$ $\displaystyle \ D_4 =${$\displaystyle {1 , \sigma , \sigma ^{2}, \sigma ^{3}, \tau , \sigma \tau , \sigma ^{2} \tau , \sigma ^{3} \tau }$}

(3) Find $\displaystyle < \sigma^{2} , \tau > \ \mbox{and} \ <\sigma^{3} , \sigma \tau >$?

(4) What are the left cosets of $\displaystyle <\tau>, <\sigma^{2}>, \mbox{and} \ <\sigma^{2}, \tau>$?

(5) Prove if $\displaystyle <\tau> \ \mbox{and/or} \ <\sigma^{2}>$ is normal.

(6) Construct the Cayley table of $\displaystyle g/<\tau>$

I've tried really hard to work these questions out. I worked out the first two questions (from the attached image above) but I'm having trouble with the four posted here. I really need to be shown how to do these otherwise I wont get it. Ive been working on these for about 6 hours and Im not getting anywhere. (Crying)
• Apr 26th 2009, 06:51 PM
TheEmptySet
$\displaystyle D_8 \mbox{ or } D_4$ is the example you are looking for