Is $X + frac{2}{X}$ a rational quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?












2












$begingroup$


First of all, I apologize for the rather silly question. This came up while I was scouring the Internet on a mathematical terminology appropriate for a concept that I need for a paper which I am currently writing.



So here it is:




Is $X + frac{2}{X}$ a rational quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




Or to put in another way:




Can the rational function $X + frac{2}{X}$ be represented by a quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




I know that I can just check Cassels' Rational Quadratic Forms, unfortunately the nearest university library is a bit far from my place of residence (not to mention being closed during the holidays).










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$endgroup$












  • $begingroup$
    @flawr: I would go with the definition in Wikipedia, although honestly, I was not able to spot an actual definition for rational quadratic form but only for quadratic form per se.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Dec 31 '18 at 9:41










  • $begingroup$
    My apologies! I meant to say $X in mathbb{Q} setminus mathbb{Z}$. Editing my question now to reflect this change.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Jan 25 at 8:09


















2












$begingroup$


First of all, I apologize for the rather silly question. This came up while I was scouring the Internet on a mathematical terminology appropriate for a concept that I need for a paper which I am currently writing.



So here it is:




Is $X + frac{2}{X}$ a rational quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




Or to put in another way:




Can the rational function $X + frac{2}{X}$ be represented by a quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




I know that I can just check Cassels' Rational Quadratic Forms, unfortunately the nearest university library is a bit far from my place of residence (not to mention being closed during the holidays).










share|cite|improve this question











$endgroup$












  • $begingroup$
    @flawr: I would go with the definition in Wikipedia, although honestly, I was not able to spot an actual definition for rational quadratic form but only for quadratic form per se.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Dec 31 '18 at 9:41










  • $begingroup$
    My apologies! I meant to say $X in mathbb{Q} setminus mathbb{Z}$. Editing my question now to reflect this change.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Jan 25 at 8:09
















2












2








2





$begingroup$


First of all, I apologize for the rather silly question. This came up while I was scouring the Internet on a mathematical terminology appropriate for a concept that I need for a paper which I am currently writing.



So here it is:




Is $X + frac{2}{X}$ a rational quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




Or to put in another way:




Can the rational function $X + frac{2}{X}$ be represented by a quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




I know that I can just check Cassels' Rational Quadratic Forms, unfortunately the nearest university library is a bit far from my place of residence (not to mention being closed during the holidays).










share|cite|improve this question











$endgroup$




First of all, I apologize for the rather silly question. This came up while I was scouring the Internet on a mathematical terminology appropriate for a concept that I need for a paper which I am currently writing.



So here it is:




Is $X + frac{2}{X}$ a rational quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




Or to put in another way:




Can the rational function $X + frac{2}{X}$ be represented by a quadratic form, where $X in mathbb{Q} setminus mathbb{Z}$?




I know that I can just check Cassels' Rational Quadratic Forms, unfortunately the nearest university library is a bit far from my place of residence (not to mention being closed during the holidays).







quadratic-forms representations-by-quadratic-forms






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 25 at 8:10







Jose Arnaldo Bebita-Dris

















asked Dec 31 '18 at 8:50









Jose Arnaldo Bebita-DrisJose Arnaldo Bebita-Dris

5,27452045




5,27452045












  • $begingroup$
    @flawr: I would go with the definition in Wikipedia, although honestly, I was not able to spot an actual definition for rational quadratic form but only for quadratic form per se.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Dec 31 '18 at 9:41










  • $begingroup$
    My apologies! I meant to say $X in mathbb{Q} setminus mathbb{Z}$. Editing my question now to reflect this change.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Jan 25 at 8:09




















  • $begingroup$
    @flawr: I would go with the definition in Wikipedia, although honestly, I was not able to spot an actual definition for rational quadratic form but only for quadratic form per se.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Dec 31 '18 at 9:41










  • $begingroup$
    My apologies! I meant to say $X in mathbb{Q} setminus mathbb{Z}$. Editing my question now to reflect this change.
    $endgroup$
    – Jose Arnaldo Bebita-Dris
    Jan 25 at 8:09


















$begingroup$
@flawr: I would go with the definition in Wikipedia, although honestly, I was not able to spot an actual definition for rational quadratic form but only for quadratic form per se.
$endgroup$
– Jose Arnaldo Bebita-Dris
Dec 31 '18 at 9:41




$begingroup$
@flawr: I would go with the definition in Wikipedia, although honestly, I was not able to spot an actual definition for rational quadratic form but only for quadratic form per se.
$endgroup$
– Jose Arnaldo Bebita-Dris
Dec 31 '18 at 9:41












$begingroup$
My apologies! I meant to say $X in mathbb{Q} setminus mathbb{Z}$. Editing my question now to reflect this change.
$endgroup$
– Jose Arnaldo Bebita-Dris
Jan 25 at 8:09






$begingroup$
My apologies! I meant to say $X in mathbb{Q} setminus mathbb{Z}$. Editing my question now to reflect this change.
$endgroup$
– Jose Arnaldo Bebita-Dris
Jan 25 at 8:09












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