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Consider $R=k[x_1,x_2,…x_n]$. Difference between $(f_1,..,f_k)$ and $k[f_1,…f_k]$


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I'm confused on the difference between these two objects. My book says that we can see the difference when considering the simple case where $f_1=x^2in k[x]$, and see that $1in k[x^2]$, but $1notin (x^2)$.



However I couldn't figure out why $1in k[x^2]$. Could anyone help illustrate this?










share|cite|improve this question









$endgroup$

















    2












    $begingroup$


    I'm confused on the difference between these two objects. My book says that we can see the difference when considering the simple case where $f_1=x^2in k[x]$, and see that $1in k[x^2]$, but $1notin (x^2)$.



    However I couldn't figure out why $1in k[x^2]$. Could anyone help illustrate this?










    share|cite|improve this question









    $endgroup$















      2












      2








      2





      $begingroup$


      I'm confused on the difference between these two objects. My book says that we can see the difference when considering the simple case where $f_1=x^2in k[x]$, and see that $1in k[x^2]$, but $1notin (x^2)$.



      However I couldn't figure out why $1in k[x^2]$. Could anyone help illustrate this?










      share|cite|improve this question









      $endgroup$




      I'm confused on the difference between these two objects. My book says that we can see the difference when considering the simple case where $f_1=x^2in k[x]$, and see that $1in k[x^2]$, but $1notin (x^2)$.



      However I couldn't figure out why $1in k[x^2]$. Could anyone help illustrate this?







      abstract-algebra ring-theory






      share|cite|improve this question













      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Mar 12 at 22:30









      davidhdavidh

      3178




      3178






















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          $begingroup$

          $k[x^2]$ denotes the set of polynomials in $x^2$ with coefficients in the field $k$, i.e. the set of (ordinary) polynomials with only monomials of even degree (+0). $1$ has degree $0$, as all non-zero constants, and if I remember well, $0$ is even. So $1$ belongs to $k[x^2]$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            lol, yeah that makes sense. Thanks.
            $endgroup$
            – davidh
            Mar 12 at 22:48











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          $begingroup$

          $k[x^2]$ denotes the set of polynomials in $x^2$ with coefficients in the field $k$, i.e. the set of (ordinary) polynomials with only monomials of even degree (+0). $1$ has degree $0$, as all non-zero constants, and if I remember well, $0$ is even. So $1$ belongs to $k[x^2]$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            lol, yeah that makes sense. Thanks.
            $endgroup$
            – davidh
            Mar 12 at 22:48
















          4












          $begingroup$

          $k[x^2]$ denotes the set of polynomials in $x^2$ with coefficients in the field $k$, i.e. the set of (ordinary) polynomials with only monomials of even degree (+0). $1$ has degree $0$, as all non-zero constants, and if I remember well, $0$ is even. So $1$ belongs to $k[x^2]$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            lol, yeah that makes sense. Thanks.
            $endgroup$
            – davidh
            Mar 12 at 22:48














          4












          4








          4





          $begingroup$

          $k[x^2]$ denotes the set of polynomials in $x^2$ with coefficients in the field $k$, i.e. the set of (ordinary) polynomials with only monomials of even degree (+0). $1$ has degree $0$, as all non-zero constants, and if I remember well, $0$ is even. So $1$ belongs to $k[x^2]$.






          share|cite|improve this answer









          $endgroup$



          $k[x^2]$ denotes the set of polynomials in $x^2$ with coefficients in the field $k$, i.e. the set of (ordinary) polynomials with only monomials of even degree (+0). $1$ has degree $0$, as all non-zero constants, and if I remember well, $0$ is even. So $1$ belongs to $k[x^2]$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Mar 12 at 22:42









          BernardBernard

          123k741117




          123k741117












          • $begingroup$
            lol, yeah that makes sense. Thanks.
            $endgroup$
            – davidh
            Mar 12 at 22:48


















          • $begingroup$
            lol, yeah that makes sense. Thanks.
            $endgroup$
            – davidh
            Mar 12 at 22:48
















          $begingroup$
          lol, yeah that makes sense. Thanks.
          $endgroup$
          – davidh
          Mar 12 at 22:48




          $begingroup$
          lol, yeah that makes sense. Thanks.
          $endgroup$
          – davidh
          Mar 12 at 22:48


















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