on the order of derived subgroup

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Let $P=M_p^n+1=langle a,b mid a^p^n=b^p=1, a^b=a^1+p^n-1rangle$.
I want to prove that $P^prime=langle [a,b] rangle$.



My Try: Clearly $langle [a,b] rangle le P^prime$. Put $K:=langle [a,b ]rangle$. Since $a^b=a^1+p^n-1$, we have
$[a,b]=a^p^n-1$. Thus $K rm char langle a rangle trianglelefteq P$, and so $K trianglelefteq P$. Consider $P/K$. If $P/K$ is abelian, then we do. Please help me to complete it.







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    The images of the generators $a$ and $b$ of $P$ commute in $P/K$, because $[a,b] in K$. If the generators of a group commute with each other, then the group is abelian.
    – Derek Holt
    Aug 26 at 10:32










  • @Derek Holt Thanks. Really, $P/K=langle aK,bK rangle$. Thats right?
    – Little girl
    Aug 26 at 10:34















up vote
3
down vote

favorite












Let $P=M_p^n+1=langle a,b mid a^p^n=b^p=1, a^b=a^1+p^n-1rangle$.
I want to prove that $P^prime=langle [a,b] rangle$.



My Try: Clearly $langle [a,b] rangle le P^prime$. Put $K:=langle [a,b ]rangle$. Since $a^b=a^1+p^n-1$, we have
$[a,b]=a^p^n-1$. Thus $K rm char langle a rangle trianglelefteq P$, and so $K trianglelefteq P$. Consider $P/K$. If $P/K$ is abelian, then we do. Please help me to complete it.







share|cite|improve this question


















  • 3




    The images of the generators $a$ and $b$ of $P$ commute in $P/K$, because $[a,b] in K$. If the generators of a group commute with each other, then the group is abelian.
    – Derek Holt
    Aug 26 at 10:32










  • @Derek Holt Thanks. Really, $P/K=langle aK,bK rangle$. Thats right?
    – Little girl
    Aug 26 at 10:34













up vote
3
down vote

favorite









up vote
3
down vote

favorite











Let $P=M_p^n+1=langle a,b mid a^p^n=b^p=1, a^b=a^1+p^n-1rangle$.
I want to prove that $P^prime=langle [a,b] rangle$.



My Try: Clearly $langle [a,b] rangle le P^prime$. Put $K:=langle [a,b ]rangle$. Since $a^b=a^1+p^n-1$, we have
$[a,b]=a^p^n-1$. Thus $K rm char langle a rangle trianglelefteq P$, and so $K trianglelefteq P$. Consider $P/K$. If $P/K$ is abelian, then we do. Please help me to complete it.







share|cite|improve this question














Let $P=M_p^n+1=langle a,b mid a^p^n=b^p=1, a^b=a^1+p^n-1rangle$.
I want to prove that $P^prime=langle [a,b] rangle$.



My Try: Clearly $langle [a,b] rangle le P^prime$. Put $K:=langle [a,b ]rangle$. Since $a^b=a^1+p^n-1$, we have
$[a,b]=a^p^n-1$. Thus $K rm char langle a rangle trianglelefteq P$, and so $K trianglelefteq P$. Consider $P/K$. If $P/K$ is abelian, then we do. Please help me to complete it.









share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Aug 26 at 11:47









Shaun

7,43692972




7,43692972










asked Aug 26 at 10:27









Little girl

1768




1768







  • 3




    The images of the generators $a$ and $b$ of $P$ commute in $P/K$, because $[a,b] in K$. If the generators of a group commute with each other, then the group is abelian.
    – Derek Holt
    Aug 26 at 10:32










  • @Derek Holt Thanks. Really, $P/K=langle aK,bK rangle$. Thats right?
    – Little girl
    Aug 26 at 10:34













  • 3




    The images of the generators $a$ and $b$ of $P$ commute in $P/K$, because $[a,b] in K$. If the generators of a group commute with each other, then the group is abelian.
    – Derek Holt
    Aug 26 at 10:32










  • @Derek Holt Thanks. Really, $P/K=langle aK,bK rangle$. Thats right?
    – Little girl
    Aug 26 at 10:34








3




3




The images of the generators $a$ and $b$ of $P$ commute in $P/K$, because $[a,b] in K$. If the generators of a group commute with each other, then the group is abelian.
– Derek Holt
Aug 26 at 10:32




The images of the generators $a$ and $b$ of $P$ commute in $P/K$, because $[a,b] in K$. If the generators of a group commute with each other, then the group is abelian.
– Derek Holt
Aug 26 at 10:32












@Derek Holt Thanks. Really, $P/K=langle aK,bK rangle$. Thats right?
– Little girl
Aug 26 at 10:34





@Derek Holt Thanks. Really, $P/K=langle aK,bK rangle$. Thats right?
– Little girl
Aug 26 at 10:34
















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