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 September 14th, 2017, 03:08 PM #1 Member   Joined: Jan 2015 From: usa Posts: 79 Thanks: 0 automophism I want to show that there exists an automorphism $\phi$ of $Q_8$ such that $\phi(\sigma)=\nu$ and $\phi(\nu)=\sigma\nu$. Where $\sigma=\begin{pmatrix}e^{\pi \frac{i}{2}}&0\\0&e^{-\pi \frac{i}{2}}\end{pmatrix}$ and $\nu=\begin{pmatrix}0&1\\-1&0\end{pmatrix}$ Thanks for your help in advance Last edited by mona123; September 14th, 2017 at 03:19 PM.
 September 14th, 2017, 03:15 PM #2 Senior Member   Joined: Aug 2012 Posts: 1,661 Thanks: 427 What work have you done on the problem? Where are you stuck? Have you written down the exact definition of each technical term in the problem? Have you written down exactly what it is you're being asked to show? These steps are essential in every problem you will encounter at this level of math.
 September 14th, 2017, 03:28 PM #3 Member   Joined: Jan 2015 From: usa Posts: 79 Thanks: 0 I have noticed only that $\phi(\nu)=\sigma\phi(\sigma)$ but i can't answer the problem, please help me i will be grateful if you do so. Last edited by greg1313; September 14th, 2017 at 05:49 PM.
 September 29th, 2017, 06:19 AM #4 Math Team   Joined: Jan 2015 From: Alabama Posts: 2,876 Thanks: 766 The first thing I would do is calculate that $\displaystyle \sigma\nu= \begin{pmatrix}e^{\pi\frac{i}{2}} & 0 \\ 0 & e^{-\pi\frac{i}{2}}\end{pmatrix}\begin{pmatrix}0 & 1 \\ -1 & 0 \end{pmatrix}= \begin{pmatrix}0 & e^{\pi\frac{i}{2}} \\ -e^{-\pi\frac{i}{2}} & 0 \end{pmatrix}$. So you want $\displaystyle \phi$ that maps $\displaystyle \begin{pmatrix}e^{\pi\frac{i}{2}} & 0 \\ 0 & e^{-\pi\frac{i}{2}}\end{pmatrix}$ to $\displaystyle \begin{pmatrix}0 & 1 \\ -1 & 0 \end{pmatrix}$ and maps $\displaystyle \begin{pmatrix}0 & 1 \\ -1 & 0 \end{pmatrix}$ to $\displaystyle \begin{pmatrix}0 & e^{\pi\frac{i}{2}} \\ -e^{-\pi\frac{i}{2}} & 0 \end{pmatrix}$.

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