Example of polynomial in two variables











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Can you please give me an example of a polynomial $F in K[X,Y]$ such that $V(F)$ is finite?



I found in Fulton the following proposition:




If F is an irreducible polynomial in $K[X,Y]$ such that $V(F)$ is infinite, then $I(V(F))=(F)$, and $V(F)$ is irreducible.





Is the condition $V(F)$ is infinite necessarily?



Thank you!










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    up vote
    0
    down vote

    favorite












    Can you please give me an example of a polynomial $F in K[X,Y]$ such that $V(F)$ is finite?



    I found in Fulton the following proposition:




    If F is an irreducible polynomial in $K[X,Y]$ such that $V(F)$ is infinite, then $I(V(F))=(F)$, and $V(F)$ is irreducible.





    Is the condition $V(F)$ is infinite necessarily?



    Thank you!










    share|cite|improve this question
























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      Can you please give me an example of a polynomial $F in K[X,Y]$ such that $V(F)$ is finite?



      I found in Fulton the following proposition:




      If F is an irreducible polynomial in $K[X,Y]$ such that $V(F)$ is infinite, then $I(V(F))=(F)$, and $V(F)$ is irreducible.





      Is the condition $V(F)$ is infinite necessarily?



      Thank you!










      share|cite|improve this question













      Can you please give me an example of a polynomial $F in K[X,Y]$ such that $V(F)$ is finite?



      I found in Fulton the following proposition:




      If F is an irreducible polynomial in $K[X,Y]$ such that $V(F)$ is infinite, then $I(V(F))=(F)$, and $V(F)$ is irreducible.





      Is the condition $V(F)$ is infinite necessarily?



      Thank you!







      algebraic-geometry polynomials irreducible-polynomials






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      asked Nov 17 at 7:52









      mip

      344




      344






















          2 Answers
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          down vote



          accepted










          Take $K = mathbb{R}$ and $F(X,Y) = X^2 + Y^2$.






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            up vote
            2
            down vote













            Here's a very easy way: take $K$ to be a finite field and $F$ to be any polynomial in $K[X,Y]$.






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              2 Answers
              2






              active

              oldest

              votes








              2 Answers
              2






              active

              oldest

              votes









              active

              oldest

              votes






              active

              oldest

              votes








              up vote
              2
              down vote



              accepted










              Take $K = mathbb{R}$ and $F(X,Y) = X^2 + Y^2$.






              share|cite|improve this answer

























                up vote
                2
                down vote



                accepted










                Take $K = mathbb{R}$ and $F(X,Y) = X^2 + Y^2$.






                share|cite|improve this answer























                  up vote
                  2
                  down vote



                  accepted







                  up vote
                  2
                  down vote



                  accepted






                  Take $K = mathbb{R}$ and $F(X,Y) = X^2 + Y^2$.






                  share|cite|improve this answer












                  Take $K = mathbb{R}$ and $F(X,Y) = X^2 + Y^2$.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered Nov 17 at 7:56









                  Sasha

                  4,09339




                  4,09339






















                      up vote
                      2
                      down vote













                      Here's a very easy way: take $K$ to be a finite field and $F$ to be any polynomial in $K[X,Y]$.






                      share|cite|improve this answer

























                        up vote
                        2
                        down vote













                        Here's a very easy way: take $K$ to be a finite field and $F$ to be any polynomial in $K[X,Y]$.






                        share|cite|improve this answer























                          up vote
                          2
                          down vote










                          up vote
                          2
                          down vote









                          Here's a very easy way: take $K$ to be a finite field and $F$ to be any polynomial in $K[X,Y]$.






                          share|cite|improve this answer












                          Here's a very easy way: take $K$ to be a finite field and $F$ to be any polynomial in $K[X,Y]$.







                          share|cite|improve this answer












                          share|cite|improve this answer



                          share|cite|improve this answer










                          answered Nov 17 at 17:01









                          André 3000

                          12.2k22041




                          12.2k22041






























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