Prove that $3$ is prime in $mathbb Q(i)$ but not in $mathbb Q(√6)$ [closed] Announcing the...

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Prove that $3$ is prime in $mathbb Q(i)$ but not in $mathbb Q(√6)$ [closed]



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)Prove 3 is prime in the ring $Bbb{Z[i]}$.Show that $3$ is not a prime in $mathbb Q[sqrt{7}]$Correspondence between valuations and prime idealsNorm of Prime IdealFalse proof: no element has a prime norm in the ring $mathbb Z[zeta_p]$possible norms of prime ideals in the class group of $K=mathbb{Q}(sqrt{-21})$confusion with calculating the ideal class group of a quadratic fieldCalculating the class numberFinding all the ideals of a given prime normDoes the prime ideal with its norm a power of prime exist? where $p$ is a prime number.If $mathcal{O}_{Bbb{Q}(sqrt{d})}$ has class number $2$ or higher, does that mean $sqrt{d}$ is irreducible but not prime?The prime ideal in a number ring












3












$begingroup$


I m confused a little bit helps me to get out of this
As I know if the norm of a given number is prime then that number is prime










share|cite|improve this question











$endgroup$



closed as off-topic by Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos Mar 26 at 13:45


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos

If this question can be reworded to fit the rules in the help center, please edit the question.












  • 5




    $begingroup$
    This has been explained nicely on this site. First $3$ is prime in $Bbb Q(i)$, see here. In $Bbb Q(sqrt{6})$ however, $3=(3+sqrt{6})(3-sqrt{6})$. For an almost duplicate of this, see here.
    $endgroup$
    – Dietrich Burde
    Mar 26 at 9:05








  • 3




    $begingroup$
    You probably mean $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ instead?
    $endgroup$
    – Henno Brandsma
    Mar 26 at 9:08
















3












$begingroup$


I m confused a little bit helps me to get out of this
As I know if the norm of a given number is prime then that number is prime










share|cite|improve this question











$endgroup$



closed as off-topic by Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos Mar 26 at 13:45


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos

If this question can be reworded to fit the rules in the help center, please edit the question.












  • 5




    $begingroup$
    This has been explained nicely on this site. First $3$ is prime in $Bbb Q(i)$, see here. In $Bbb Q(sqrt{6})$ however, $3=(3+sqrt{6})(3-sqrt{6})$. For an almost duplicate of this, see here.
    $endgroup$
    – Dietrich Burde
    Mar 26 at 9:05








  • 3




    $begingroup$
    You probably mean $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ instead?
    $endgroup$
    – Henno Brandsma
    Mar 26 at 9:08














3












3








3





$begingroup$


I m confused a little bit helps me to get out of this
As I know if the norm of a given number is prime then that number is prime










share|cite|improve this question











$endgroup$




I m confused a little bit helps me to get out of this
As I know if the norm of a given number is prime then that number is prime







algebraic-number-theory






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 26 at 10:12









YuiTo Cheng

2,65641037




2,65641037










asked Mar 26 at 9:02









lone aazam lone aazam

162




162




closed as off-topic by Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos Mar 26 at 13:45


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos

If this question can be reworded to fit the rules in the help center, please edit the question.







closed as off-topic by Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos Mar 26 at 13:45


This question appears to be off-topic. The users who voted to close gave this specific reason:


  • "This question is missing context or other details: Please provide additional context, which ideally explains why the question is relevant to you and our community. Some forms of context include: background and motivation, relevant definitions, source, possible strategies, your current progress, why the question is interesting or important, etc." – Saad, Dietrich Burde, Riccardo.Alestra, YiFan, José Carlos Santos

If this question can be reworded to fit the rules in the help center, please edit the question.








  • 5




    $begingroup$
    This has been explained nicely on this site. First $3$ is prime in $Bbb Q(i)$, see here. In $Bbb Q(sqrt{6})$ however, $3=(3+sqrt{6})(3-sqrt{6})$. For an almost duplicate of this, see here.
    $endgroup$
    – Dietrich Burde
    Mar 26 at 9:05








  • 3




    $begingroup$
    You probably mean $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ instead?
    $endgroup$
    – Henno Brandsma
    Mar 26 at 9:08














  • 5




    $begingroup$
    This has been explained nicely on this site. First $3$ is prime in $Bbb Q(i)$, see here. In $Bbb Q(sqrt{6})$ however, $3=(3+sqrt{6})(3-sqrt{6})$. For an almost duplicate of this, see here.
    $endgroup$
    – Dietrich Burde
    Mar 26 at 9:05








  • 3




    $begingroup$
    You probably mean $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ instead?
    $endgroup$
    – Henno Brandsma
    Mar 26 at 9:08








5




5




$begingroup$
This has been explained nicely on this site. First $3$ is prime in $Bbb Q(i)$, see here. In $Bbb Q(sqrt{6})$ however, $3=(3+sqrt{6})(3-sqrt{6})$. For an almost duplicate of this, see here.
$endgroup$
– Dietrich Burde
Mar 26 at 9:05






$begingroup$
This has been explained nicely on this site. First $3$ is prime in $Bbb Q(i)$, see here. In $Bbb Q(sqrt{6})$ however, $3=(3+sqrt{6})(3-sqrt{6})$. For an almost duplicate of this, see here.
$endgroup$
– Dietrich Burde
Mar 26 at 9:05






3




3




$begingroup$
You probably mean $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ instead?
$endgroup$
– Henno Brandsma
Mar 26 at 9:08




$begingroup$
You probably mean $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ instead?
$endgroup$
– Henno Brandsma
Mar 26 at 9:08










1 Answer
1






active

oldest

votes


















2












$begingroup$

We're working in general rings, not just in $mathbb{Z}$, which is where you first encountered the notion of a prime element.



An element $p$ of a (commutative unitary) ring $R$ is prime iff $forall x,y in R: p | xy implies p|x text{ or } p|y$. Because we quantify over $R$ this very much depends on the ring we're working in. And (confusingly?) $3=1+1+1$ is a member of $mathbb{Z}$, $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ and many more rings and for all of these we can ask "is $3$ prime in that ring"? and we get different answers for different rings.



See the comments for links to previous answers, which I won't copy here.






share|cite|improve this answer











$endgroup$




















    1 Answer
    1






    active

    oldest

    votes








    1 Answer
    1






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    2












    $begingroup$

    We're working in general rings, not just in $mathbb{Z}$, which is where you first encountered the notion of a prime element.



    An element $p$ of a (commutative unitary) ring $R$ is prime iff $forall x,y in R: p | xy implies p|x text{ or } p|y$. Because we quantify over $R$ this very much depends on the ring we're working in. And (confusingly?) $3=1+1+1$ is a member of $mathbb{Z}$, $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ and many more rings and for all of these we can ask "is $3$ prime in that ring"? and we get different answers for different rings.



    See the comments for links to previous answers, which I won't copy here.






    share|cite|improve this answer











    $endgroup$


















      2












      $begingroup$

      We're working in general rings, not just in $mathbb{Z}$, which is where you first encountered the notion of a prime element.



      An element $p$ of a (commutative unitary) ring $R$ is prime iff $forall x,y in R: p | xy implies p|x text{ or } p|y$. Because we quantify over $R$ this very much depends on the ring we're working in. And (confusingly?) $3=1+1+1$ is a member of $mathbb{Z}$, $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ and many more rings and for all of these we can ask "is $3$ prime in that ring"? and we get different answers for different rings.



      See the comments for links to previous answers, which I won't copy here.






      share|cite|improve this answer











      $endgroup$
















        2












        2








        2





        $begingroup$

        We're working in general rings, not just in $mathbb{Z}$, which is where you first encountered the notion of a prime element.



        An element $p$ of a (commutative unitary) ring $R$ is prime iff $forall x,y in R: p | xy implies p|x text{ or } p|y$. Because we quantify over $R$ this very much depends on the ring we're working in. And (confusingly?) $3=1+1+1$ is a member of $mathbb{Z}$, $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ and many more rings and for all of these we can ask "is $3$ prime in that ring"? and we get different answers for different rings.



        See the comments for links to previous answers, which I won't copy here.






        share|cite|improve this answer











        $endgroup$



        We're working in general rings, not just in $mathbb{Z}$, which is where you first encountered the notion of a prime element.



        An element $p$ of a (commutative unitary) ring $R$ is prime iff $forall x,y in R: p | xy implies p|x text{ or } p|y$. Because we quantify over $R$ this very much depends on the ring we're working in. And (confusingly?) $3=1+1+1$ is a member of $mathbb{Z}$, $mathbb{Z}[i]$ and $mathbb{Z}[sqrt{6}]$ and many more rings and for all of these we can ask "is $3$ prime in that ring"? and we get different answers for different rings.



        See the comments for links to previous answers, which I won't copy here.







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited Mar 26 at 10:19









        J. W. Tanner

        5,0851520




        5,0851520










        answered Mar 26 at 9:13









        Henno BrandsmaHenno Brandsma

        117k350128




        117k350128















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