Using Cardano's method to find an algebraic equation whose root is $sqrt{2} +sqrt[3]{3}$ ...

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Using Cardano's method to find an algebraic equation whose root is $sqrt{2} +sqrt[3]{3}$



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)What equation intersects only once with $f(x)=sqrt{1-(x-2)^2}$Find all $qinmathbb{Q}$ such that $ qx^2+(q+1)x+q=1 $ has integer solutions.Solve the simultaneous equations $x + frac{3x-y}{x^2+y^2} = 3 $, $ y – frac{x+3y}{x^2+y^2} = 0$Finding a general solution for {sin(x)=sqrt(3)/2 , cos(x)=-0.5} using an algebraic methodFinding transcendental roots to an algebraic equationFind the number of solutions of the equationMinimum degree rational equation with root $a+sqrt{b}+sqrt{c}+sqrt{d}$.About Cardano's formula and the cubic equationFind an equation of the parabola with zeros $0$ and $6$ and a minimum value of $-9$Find the rational solution of the equation












1












$begingroup$


$sqrt{2} +sqrt[3]{3}$ solution of an algebraic equation $ a_{0}x^{n}+a_{1}x^{n-1}+a_{2}x^{n-2}+cdots+a_{0}=0 $



How to find this equation?
I tried Cardano's method, noting that
$$sqrt{2} +sqrt[3]{3} = sqrt[3]{sqrt{8}} +sqrt[3]{3}$$



It means
$$begin{align}
-frac{q}{2}+sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=3 \[4pt]
-frac{q}{2}-sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=sqrt{8}
end{align}$$



but this system doesn't have natural solutions.



Maybe it has rational $p$ and $q$?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Use the method given in Example 4 on p. 3 of this old class handout of mine.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:34






  • 1




    $begingroup$
    By the way, the context of your question is not clear. Do you simply want to know a method for finding such an algebraic equation (with integer coefficients, something you neglected to say by the way), or do you want to find a method that BEGINS with Cardano's formula? I don't think beginning with Cardano's formula will help much because one can show (with some work) that there is no cubic polynomial with integer coefficients that has $sqrt{2} + sqrt[3]{3}$ as a root.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:44








  • 1




    $begingroup$
    The minimal polynomial for $sqrt{2}+sqrt[3]{3}$ is has degree 6, so Cardano's method of solving cubic equations won't be any help.
    $endgroup$
    – Blue
    Mar 23 at 13:11










  • $begingroup$
    Thank you very much
    $endgroup$
    – demsp
    Mar 23 at 20:26
















1












$begingroup$


$sqrt{2} +sqrt[3]{3}$ solution of an algebraic equation $ a_{0}x^{n}+a_{1}x^{n-1}+a_{2}x^{n-2}+cdots+a_{0}=0 $



How to find this equation?
I tried Cardano's method, noting that
$$sqrt{2} +sqrt[3]{3} = sqrt[3]{sqrt{8}} +sqrt[3]{3}$$



It means
$$begin{align}
-frac{q}{2}+sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=3 \[4pt]
-frac{q}{2}-sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=sqrt{8}
end{align}$$



but this system doesn't have natural solutions.



Maybe it has rational $p$ and $q$?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Use the method given in Example 4 on p. 3 of this old class handout of mine.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:34






  • 1




    $begingroup$
    By the way, the context of your question is not clear. Do you simply want to know a method for finding such an algebraic equation (with integer coefficients, something you neglected to say by the way), or do you want to find a method that BEGINS with Cardano's formula? I don't think beginning with Cardano's formula will help much because one can show (with some work) that there is no cubic polynomial with integer coefficients that has $sqrt{2} + sqrt[3]{3}$ as a root.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:44








  • 1




    $begingroup$
    The minimal polynomial for $sqrt{2}+sqrt[3]{3}$ is has degree 6, so Cardano's method of solving cubic equations won't be any help.
    $endgroup$
    – Blue
    Mar 23 at 13:11










  • $begingroup$
    Thank you very much
    $endgroup$
    – demsp
    Mar 23 at 20:26














1












1








1





$begingroup$


$sqrt{2} +sqrt[3]{3}$ solution of an algebraic equation $ a_{0}x^{n}+a_{1}x^{n-1}+a_{2}x^{n-2}+cdots+a_{0}=0 $



How to find this equation?
I tried Cardano's method, noting that
$$sqrt{2} +sqrt[3]{3} = sqrt[3]{sqrt{8}} +sqrt[3]{3}$$



It means
$$begin{align}
-frac{q}{2}+sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=3 \[4pt]
-frac{q}{2}-sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=sqrt{8}
end{align}$$



but this system doesn't have natural solutions.



Maybe it has rational $p$ and $q$?










share|cite|improve this question











$endgroup$




$sqrt{2} +sqrt[3]{3}$ solution of an algebraic equation $ a_{0}x^{n}+a_{1}x^{n-1}+a_{2}x^{n-2}+cdots+a_{0}=0 $



How to find this equation?
I tried Cardano's method, noting that
$$sqrt{2} +sqrt[3]{3} = sqrt[3]{sqrt{8}} +sqrt[3]{3}$$



It means
$$begin{align}
-frac{q}{2}+sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=3 \[4pt]
-frac{q}{2}-sqrt{ frac{q^{2}}{4}+frac{p^{3}}{27}}&=sqrt{8}
end{align}$$



but this system doesn't have natural solutions.



Maybe it has rational $p$ and $q$?







algebra-precalculus






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 23 at 13:08









Blue

49.7k870158




49.7k870158










asked Mar 23 at 12:19









demspdemsp

103




103












  • $begingroup$
    Use the method given in Example 4 on p. 3 of this old class handout of mine.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:34






  • 1




    $begingroup$
    By the way, the context of your question is not clear. Do you simply want to know a method for finding such an algebraic equation (with integer coefficients, something you neglected to say by the way), or do you want to find a method that BEGINS with Cardano's formula? I don't think beginning with Cardano's formula will help much because one can show (with some work) that there is no cubic polynomial with integer coefficients that has $sqrt{2} + sqrt[3]{3}$ as a root.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:44








  • 1




    $begingroup$
    The minimal polynomial for $sqrt{2}+sqrt[3]{3}$ is has degree 6, so Cardano's method of solving cubic equations won't be any help.
    $endgroup$
    – Blue
    Mar 23 at 13:11










  • $begingroup$
    Thank you very much
    $endgroup$
    – demsp
    Mar 23 at 20:26


















  • $begingroup$
    Use the method given in Example 4 on p. 3 of this old class handout of mine.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:34






  • 1




    $begingroup$
    By the way, the context of your question is not clear. Do you simply want to know a method for finding such an algebraic equation (with integer coefficients, something you neglected to say by the way), or do you want to find a method that BEGINS with Cardano's formula? I don't think beginning with Cardano's formula will help much because one can show (with some work) that there is no cubic polynomial with integer coefficients that has $sqrt{2} + sqrt[3]{3}$ as a root.
    $endgroup$
    – Dave L. Renfro
    Mar 23 at 12:44








  • 1




    $begingroup$
    The minimal polynomial for $sqrt{2}+sqrt[3]{3}$ is has degree 6, so Cardano's method of solving cubic equations won't be any help.
    $endgroup$
    – Blue
    Mar 23 at 13:11










  • $begingroup$
    Thank you very much
    $endgroup$
    – demsp
    Mar 23 at 20:26
















$begingroup$
Use the method given in Example 4 on p. 3 of this old class handout of mine.
$endgroup$
– Dave L. Renfro
Mar 23 at 12:34




$begingroup$
Use the method given in Example 4 on p. 3 of this old class handout of mine.
$endgroup$
– Dave L. Renfro
Mar 23 at 12:34




1




1




$begingroup$
By the way, the context of your question is not clear. Do you simply want to know a method for finding such an algebraic equation (with integer coefficients, something you neglected to say by the way), or do you want to find a method that BEGINS with Cardano's formula? I don't think beginning with Cardano's formula will help much because one can show (with some work) that there is no cubic polynomial with integer coefficients that has $sqrt{2} + sqrt[3]{3}$ as a root.
$endgroup$
– Dave L. Renfro
Mar 23 at 12:44






$begingroup$
By the way, the context of your question is not clear. Do you simply want to know a method for finding such an algebraic equation (with integer coefficients, something you neglected to say by the way), or do you want to find a method that BEGINS with Cardano's formula? I don't think beginning with Cardano's formula will help much because one can show (with some work) that there is no cubic polynomial with integer coefficients that has $sqrt{2} + sqrt[3]{3}$ as a root.
$endgroup$
– Dave L. Renfro
Mar 23 at 12:44






1




1




$begingroup$
The minimal polynomial for $sqrt{2}+sqrt[3]{3}$ is has degree 6, so Cardano's method of solving cubic equations won't be any help.
$endgroup$
– Blue
Mar 23 at 13:11




$begingroup$
The minimal polynomial for $sqrt{2}+sqrt[3]{3}$ is has degree 6, so Cardano's method of solving cubic equations won't be any help.
$endgroup$
– Blue
Mar 23 at 13:11












$begingroup$
Thank you very much
$endgroup$
– demsp
Mar 23 at 20:26




$begingroup$
Thank you very much
$endgroup$
– demsp
Mar 23 at 20:26










2 Answers
2






active

oldest

votes


















2












$begingroup$

Let $x=sqrt 2 + sqrt[3]{3}$. Then,
$$
x-sqrt 2 = sqrt[3]{3}
$$

Cubing both sides and rearranging we have,
$$
x^3+6x-3=sqrt 2 (3x^2+2)
$$

Squaring both sides and rearranging we have,
$$
x^6-6x^4-6x^3+12x^2-36x+1=0
$$






share|cite|improve this answer









$endgroup$





















    1












    $begingroup$

    In the same spirit as Awe Kumar Jha, let $x=sqrt 2 + sqrt[3]{3}$, that is to say
    $$x-sqrt 2 =sqrt[3]{3}implies (x-sqrt 2) ^3=3$$ Expand and group terms to get
    $$x^3-3 sqrt{2} x^2+6 x-(2 sqrt{2}+3)=0$$ Use Cardano method; it will show that this is the only real root of the equation.






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      Thank you :))))
      $endgroup$
      – demsp
      Mar 23 at 20:30












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    2 Answers
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    2 Answers
    2






    active

    oldest

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    active

    oldest

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    active

    oldest

    votes









    2












    $begingroup$

    Let $x=sqrt 2 + sqrt[3]{3}$. Then,
    $$
    x-sqrt 2 = sqrt[3]{3}
    $$

    Cubing both sides and rearranging we have,
    $$
    x^3+6x-3=sqrt 2 (3x^2+2)
    $$

    Squaring both sides and rearranging we have,
    $$
    x^6-6x^4-6x^3+12x^2-36x+1=0
    $$






    share|cite|improve this answer









    $endgroup$


















      2












      $begingroup$

      Let $x=sqrt 2 + sqrt[3]{3}$. Then,
      $$
      x-sqrt 2 = sqrt[3]{3}
      $$

      Cubing both sides and rearranging we have,
      $$
      x^3+6x-3=sqrt 2 (3x^2+2)
      $$

      Squaring both sides and rearranging we have,
      $$
      x^6-6x^4-6x^3+12x^2-36x+1=0
      $$






      share|cite|improve this answer









      $endgroup$
















        2












        2








        2





        $begingroup$

        Let $x=sqrt 2 + sqrt[3]{3}$. Then,
        $$
        x-sqrt 2 = sqrt[3]{3}
        $$

        Cubing both sides and rearranging we have,
        $$
        x^3+6x-3=sqrt 2 (3x^2+2)
        $$

        Squaring both sides and rearranging we have,
        $$
        x^6-6x^4-6x^3+12x^2-36x+1=0
        $$






        share|cite|improve this answer









        $endgroup$



        Let $x=sqrt 2 + sqrt[3]{3}$. Then,
        $$
        x-sqrt 2 = sqrt[3]{3}
        $$

        Cubing both sides and rearranging we have,
        $$
        x^3+6x-3=sqrt 2 (3x^2+2)
        $$

        Squaring both sides and rearranging we have,
        $$
        x^6-6x^4-6x^3+12x^2-36x+1=0
        $$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Mar 23 at 13:34









        Awe Kumar JhaAwe Kumar Jha

        633113




        633113























            1












            $begingroup$

            In the same spirit as Awe Kumar Jha, let $x=sqrt 2 + sqrt[3]{3}$, that is to say
            $$x-sqrt 2 =sqrt[3]{3}implies (x-sqrt 2) ^3=3$$ Expand and group terms to get
            $$x^3-3 sqrt{2} x^2+6 x-(2 sqrt{2}+3)=0$$ Use Cardano method; it will show that this is the only real root of the equation.






            share|cite|improve this answer









            $endgroup$













            • $begingroup$
              Thank you :))))
              $endgroup$
              – demsp
              Mar 23 at 20:30
















            1












            $begingroup$

            In the same spirit as Awe Kumar Jha, let $x=sqrt 2 + sqrt[3]{3}$, that is to say
            $$x-sqrt 2 =sqrt[3]{3}implies (x-sqrt 2) ^3=3$$ Expand and group terms to get
            $$x^3-3 sqrt{2} x^2+6 x-(2 sqrt{2}+3)=0$$ Use Cardano method; it will show that this is the only real root of the equation.






            share|cite|improve this answer









            $endgroup$













            • $begingroup$
              Thank you :))))
              $endgroup$
              – demsp
              Mar 23 at 20:30














            1












            1








            1





            $begingroup$

            In the same spirit as Awe Kumar Jha, let $x=sqrt 2 + sqrt[3]{3}$, that is to say
            $$x-sqrt 2 =sqrt[3]{3}implies (x-sqrt 2) ^3=3$$ Expand and group terms to get
            $$x^3-3 sqrt{2} x^2+6 x-(2 sqrt{2}+3)=0$$ Use Cardano method; it will show that this is the only real root of the equation.






            share|cite|improve this answer









            $endgroup$



            In the same spirit as Awe Kumar Jha, let $x=sqrt 2 + sqrt[3]{3}$, that is to say
            $$x-sqrt 2 =sqrt[3]{3}implies (x-sqrt 2) ^3=3$$ Expand and group terms to get
            $$x^3-3 sqrt{2} x^2+6 x-(2 sqrt{2}+3)=0$$ Use Cardano method; it will show that this is the only real root of the equation.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered Mar 23 at 15:25









            Claude LeiboviciClaude Leibovici

            126k1158135




            126k1158135












            • $begingroup$
              Thank you :))))
              $endgroup$
              – demsp
              Mar 23 at 20:30


















            • $begingroup$
              Thank you :))))
              $endgroup$
              – demsp
              Mar 23 at 20:30
















            $begingroup$
            Thank you :))))
            $endgroup$
            – demsp
            Mar 23 at 20:30




            $begingroup$
            Thank you :))))
            $endgroup$
            – demsp
            Mar 23 at 20:30


















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