Proving $X/Ycong mathbb{Z}_p^times$












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I would like to show that $X=GA_1(mathbb{Z}_p)$ has a normal subgroup $Y$ that is isomorphic to $mathbb{Z}_p$, that $X/Ycong mathbb{Z}_p^times$ but $Xnotcong mathbb{Z}_ptimes mathbb{Z}_p^times $.



$GA(mathbb{Z}_p)$ is the general affine group of matrices $1times1$ over the field $mathbb{Z}$ mod $p$ (prime) (link). Also $mathbb{Z}_p^times$ is the Multiplicative group of integers modulo $p$ (link).



I know that in order to prove $X/Ycong mathbb{Z}_p^times$ I need to find $Y$ so there is $phi : X/Y to mathbb{Z}_p^times$. But I can't think of $Y$ and $phi$ in order to solve this problem. Which group $Y$ and function $phi$ should solve it and how?










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    0












    $begingroup$


    I would like to show that $X=GA_1(mathbb{Z}_p)$ has a normal subgroup $Y$ that is isomorphic to $mathbb{Z}_p$, that $X/Ycong mathbb{Z}_p^times$ but $Xnotcong mathbb{Z}_ptimes mathbb{Z}_p^times $.



    $GA(mathbb{Z}_p)$ is the general affine group of matrices $1times1$ over the field $mathbb{Z}$ mod $p$ (prime) (link). Also $mathbb{Z}_p^times$ is the Multiplicative group of integers modulo $p$ (link).



    I know that in order to prove $X/Ycong mathbb{Z}_p^times$ I need to find $Y$ so there is $phi : X/Y to mathbb{Z}_p^times$. But I can't think of $Y$ and $phi$ in order to solve this problem. Which group $Y$ and function $phi$ should solve it and how?










    share|cite|improve this question









    $endgroup$















      0












      0








      0





      $begingroup$


      I would like to show that $X=GA_1(mathbb{Z}_p)$ has a normal subgroup $Y$ that is isomorphic to $mathbb{Z}_p$, that $X/Ycong mathbb{Z}_p^times$ but $Xnotcong mathbb{Z}_ptimes mathbb{Z}_p^times $.



      $GA(mathbb{Z}_p)$ is the general affine group of matrices $1times1$ over the field $mathbb{Z}$ mod $p$ (prime) (link). Also $mathbb{Z}_p^times$ is the Multiplicative group of integers modulo $p$ (link).



      I know that in order to prove $X/Ycong mathbb{Z}_p^times$ I need to find $Y$ so there is $phi : X/Y to mathbb{Z}_p^times$. But I can't think of $Y$ and $phi$ in order to solve this problem. Which group $Y$ and function $phi$ should solve it and how?










      share|cite|improve this question









      $endgroup$




      I would like to show that $X=GA_1(mathbb{Z}_p)$ has a normal subgroup $Y$ that is isomorphic to $mathbb{Z}_p$, that $X/Ycong mathbb{Z}_p^times$ but $Xnotcong mathbb{Z}_ptimes mathbb{Z}_p^times $.



      $GA(mathbb{Z}_p)$ is the general affine group of matrices $1times1$ over the field $mathbb{Z}$ mod $p$ (prime) (link). Also $mathbb{Z}_p^times$ is the Multiplicative group of integers modulo $p$ (link).



      I know that in order to prove $X/Ycong mathbb{Z}_p^times$ I need to find $Y$ so there is $phi : X/Y to mathbb{Z}_p^times$. But I can't think of $Y$ and $phi$ in order to solve this problem. Which group $Y$ and function $phi$ should solve it and how?







      abstract-algebra group-theory






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      asked Jan 12 at 17:13









      vesiivesii

      3978




      3978






















          1 Answer
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          0












          $begingroup$

          $newcommand{Set}[1]{left{ #1 right}}$
          It is convenient to think of $X$ as the group of matrices
          $$
          Set{begin{bmatrix}a & b\
          0 & 1end{bmatrix}
          a in mathbb{Z}_p^{times}, b in mathbb{Z}_p}.
          $$



          Hint 1




          To find $Y$, take the elements with $a = 1$.




          Hint 2




          To find $phi$, consider the map that takes the matrix $begin{bmatrix}a & b\0 & 1end{bmatrix}$ to $a$.







          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            By your hint we get $Y=left{ begin{pmatrix}1 & b\ 0 & 1 end{pmatrix}|binmathbb{Z}_{p}right}$ but why $Y=mathbb{Z}_p$ and $X/Ycongmathbb{Z}_{p}^{times}$?
            $endgroup$
            – vesii
            Jan 12 at 17:43














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          1 Answer
          1






          active

          oldest

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          active

          oldest

          votes






          active

          oldest

          votes









          0












          $begingroup$

          $newcommand{Set}[1]{left{ #1 right}}$
          It is convenient to think of $X$ as the group of matrices
          $$
          Set{begin{bmatrix}a & b\
          0 & 1end{bmatrix}
          a in mathbb{Z}_p^{times}, b in mathbb{Z}_p}.
          $$



          Hint 1




          To find $Y$, take the elements with $a = 1$.




          Hint 2




          To find $phi$, consider the map that takes the matrix $begin{bmatrix}a & b\0 & 1end{bmatrix}$ to $a$.







          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            By your hint we get $Y=left{ begin{pmatrix}1 & b\ 0 & 1 end{pmatrix}|binmathbb{Z}_{p}right}$ but why $Y=mathbb{Z}_p$ and $X/Ycongmathbb{Z}_{p}^{times}$?
            $endgroup$
            – vesii
            Jan 12 at 17:43


















          0












          $begingroup$

          $newcommand{Set}[1]{left{ #1 right}}$
          It is convenient to think of $X$ as the group of matrices
          $$
          Set{begin{bmatrix}a & b\
          0 & 1end{bmatrix}
          a in mathbb{Z}_p^{times}, b in mathbb{Z}_p}.
          $$



          Hint 1




          To find $Y$, take the elements with $a = 1$.




          Hint 2




          To find $phi$, consider the map that takes the matrix $begin{bmatrix}a & b\0 & 1end{bmatrix}$ to $a$.







          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            By your hint we get $Y=left{ begin{pmatrix}1 & b\ 0 & 1 end{pmatrix}|binmathbb{Z}_{p}right}$ but why $Y=mathbb{Z}_p$ and $X/Ycongmathbb{Z}_{p}^{times}$?
            $endgroup$
            – vesii
            Jan 12 at 17:43
















          0












          0








          0





          $begingroup$

          $newcommand{Set}[1]{left{ #1 right}}$
          It is convenient to think of $X$ as the group of matrices
          $$
          Set{begin{bmatrix}a & b\
          0 & 1end{bmatrix}
          a in mathbb{Z}_p^{times}, b in mathbb{Z}_p}.
          $$



          Hint 1




          To find $Y$, take the elements with $a = 1$.




          Hint 2




          To find $phi$, consider the map that takes the matrix $begin{bmatrix}a & b\0 & 1end{bmatrix}$ to $a$.







          share|cite|improve this answer











          $endgroup$



          $newcommand{Set}[1]{left{ #1 right}}$
          It is convenient to think of $X$ as the group of matrices
          $$
          Set{begin{bmatrix}a & b\
          0 & 1end{bmatrix}
          a in mathbb{Z}_p^{times}, b in mathbb{Z}_p}.
          $$



          Hint 1




          To find $Y$, take the elements with $a = 1$.




          Hint 2




          To find $phi$, consider the map that takes the matrix $begin{bmatrix}a & b\0 & 1end{bmatrix}$ to $a$.








          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited Jan 12 at 17:34

























          answered Jan 12 at 17:32









          Andreas CarantiAndreas Caranti

          57.3k34497




          57.3k34497












          • $begingroup$
            By your hint we get $Y=left{ begin{pmatrix}1 & b\ 0 & 1 end{pmatrix}|binmathbb{Z}_{p}right}$ but why $Y=mathbb{Z}_p$ and $X/Ycongmathbb{Z}_{p}^{times}$?
            $endgroup$
            – vesii
            Jan 12 at 17:43




















          • $begingroup$
            By your hint we get $Y=left{ begin{pmatrix}1 & b\ 0 & 1 end{pmatrix}|binmathbb{Z}_{p}right}$ but why $Y=mathbb{Z}_p$ and $X/Ycongmathbb{Z}_{p}^{times}$?
            $endgroup$
            – vesii
            Jan 12 at 17:43


















          $begingroup$
          By your hint we get $Y=left{ begin{pmatrix}1 & b\ 0 & 1 end{pmatrix}|binmathbb{Z}_{p}right}$ but why $Y=mathbb{Z}_p$ and $X/Ycongmathbb{Z}_{p}^{times}$?
          $endgroup$
          – vesii
          Jan 12 at 17:43






          $begingroup$
          By your hint we get $Y=left{ begin{pmatrix}1 & b\ 0 & 1 end{pmatrix}|binmathbb{Z}_{p}right}$ but why $Y=mathbb{Z}_p$ and $X/Ycongmathbb{Z}_{p}^{times}$?
          $endgroup$
          – vesii
          Jan 12 at 17:43




















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