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Question about a degree 5 polynomial with no rational roots


Polynomial roots of degree 2I need help proving a statement about rational rootsFourth degree polynomial with rational coefficients and a real rootNumber of roots of a polynomial of non-integer degreeQuestion about rational roots of polynomialWays to find irrational roots of an n degree polynomialHow to find polynomial functions 3rd degree with no, one, two, three zeros(roots)?Solving 5th degree polynomial






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;








2












$begingroup$


Is it possible to find a 5th degree polynomial with no rational roots, and at least one irrational root?



Edit: the polynomial must only have rational coefficients










share|cite|improve this question











$endgroup$









  • 4




    $begingroup$
    how about $(x-pi)^5$ or $(x-e)^5$ or $(x-sqrt2)^5$?
    $endgroup$
    – J. W. Tanner
    11 hours ago







  • 2




    $begingroup$
    Or even just $x^5-2$?
    $endgroup$
    – Lord Shark the Unknown
    10 hours ago

















2












$begingroup$


Is it possible to find a 5th degree polynomial with no rational roots, and at least one irrational root?



Edit: the polynomial must only have rational coefficients










share|cite|improve this question











$endgroup$









  • 4




    $begingroup$
    how about $(x-pi)^5$ or $(x-e)^5$ or $(x-sqrt2)^5$?
    $endgroup$
    – J. W. Tanner
    11 hours ago







  • 2




    $begingroup$
    Or even just $x^5-2$?
    $endgroup$
    – Lord Shark the Unknown
    10 hours ago













2












2








2





$begingroup$


Is it possible to find a 5th degree polynomial with no rational roots, and at least one irrational root?



Edit: the polynomial must only have rational coefficients










share|cite|improve this question











$endgroup$




Is it possible to find a 5th degree polynomial with no rational roots, and at least one irrational root?



Edit: the polynomial must only have rational coefficients







functions polynomials






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited 10 hours ago







Diba

















asked 11 hours ago









DibaDiba

135 bronze badges




135 bronze badges










  • 4




    $begingroup$
    how about $(x-pi)^5$ or $(x-e)^5$ or $(x-sqrt2)^5$?
    $endgroup$
    – J. W. Tanner
    11 hours ago







  • 2




    $begingroup$
    Or even just $x^5-2$?
    $endgroup$
    – Lord Shark the Unknown
    10 hours ago












  • 4




    $begingroup$
    how about $(x-pi)^5$ or $(x-e)^5$ or $(x-sqrt2)^5$?
    $endgroup$
    – J. W. Tanner
    11 hours ago







  • 2




    $begingroup$
    Or even just $x^5-2$?
    $endgroup$
    – Lord Shark the Unknown
    10 hours ago







4




4




$begingroup$
how about $(x-pi)^5$ or $(x-e)^5$ or $(x-sqrt2)^5$?
$endgroup$
– J. W. Tanner
11 hours ago





$begingroup$
how about $(x-pi)^5$ or $(x-e)^5$ or $(x-sqrt2)^5$?
$endgroup$
– J. W. Tanner
11 hours ago





2




2




$begingroup$
Or even just $x^5-2$?
$endgroup$
– Lord Shark the Unknown
10 hours ago




$begingroup$
Or even just $x^5-2$?
$endgroup$
– Lord Shark the Unknown
10 hours ago










5 Answers
5






active

oldest

votes


















4














$begingroup$

In fact we can even achieve this with a polynomial with rational coefficients: [Edit: After I wrote this answer, OP added the rationality of the coefficients as a condition.]



The Rational Root Theorem implies that $$x^5 - 2$$ has no rational roots, but since its degree is odd, it has at least one real---and hence irrational---root. (In fact, can replace $2$ here with any rational number that is not a perfect $5$th power of a rational number.)






share|cite|improve this answer











$endgroup$










  • 1




    $begingroup$
    in fact with integer coefficients
    $endgroup$
    – J. W. Tanner
    10 hours ago






  • 1




    $begingroup$
    Indeed! That said, we can always clear the denominators of any rational polynomial by multiplying by their $operatornamelcm$, and this operation preserves the roots. (But it's true that this example is a monic polynomial with integer coefficients.)
    $endgroup$
    – Travis
    10 hours ago


















1














$begingroup$

That is pretty easy, if there are not other propertys required. Just consider a polynomial like:



$(x-sqrt2)^5$






share|cite|improve this answer









$endgroup$














  • $begingroup$
    That doesn't have rational coefficients.
    $endgroup$
    – fleablood
    5 hours ago










  • $begingroup$
    @fleablood OP added the requirement that the coefficients be rational a few minutes after this answer was posted.
    $endgroup$
    – Travis
    3 hours ago


















1














$begingroup$

If $alpha$ is irrational, then the polynomial $(x-alpha)^5$ has degree $5$, and the only (repeated) root is irrational.






share|cite|improve this answer









$endgroup$










  • 2




    $begingroup$
    More generally, $(x-a_1)(x-a_2)(x-a_3)(x-a_4)(x-a_5)$ for any irrational $a_1, dots, a_5$.
    $endgroup$
    – 79037662
    10 hours ago










  • $begingroup$
    I realize now that I might have phrased the question badly- it is only considering polynomials with rational coefficients.
    $endgroup$
    – Diba
    10 hours ago






  • 1




    $begingroup$
    @DibaHeydary: In that case, see the answer by Travis
    $endgroup$
    – J. W. Tanner
    10 hours ago



















1














$begingroup$

$$ x^5 + x^4 - 4 x^3 - 3 x^2 + 3 x + 1 $$



Five real irrational roots,
$$ 2 cos left( frac2k
pi11 right) $$



enter image description here



If you prefer the roots to be $cos( 2k pi /11),$ adjust the quintic to



$$ 32x^5 + 16x^4 - 32 x^3 - 12 x^2 + 6 x + 1 $$



enter image description here



gp-pari:



? x = cos( 2 * Pi / 11)
%1 = 0.8412535328311811688618116489
? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
%2 = -1.009741959 E-28
?
? x = cos( 4 * Pi / 11)
%3 = 0.4154150130018864255292741493
? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
%4 = -2.019483917 E-28
?
? x = cos( 6 * Pi / 11)
%5 = -0.1423148382732851404437926686
? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
%6 = -7.57306469 E-29
?
? x = cos( 8 * Pi / 11)
%7 = -0.6548607339452850640569250725
? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
%8 = 0.E-28
?


=============================






share|cite|improve this answer











$endgroup$














  • $begingroup$
    I'm confused, how did you connect polynomials to triginometry? Through something like taylor series?
    $endgroup$
    – vikarjramun
    2 hours ago


















1














$begingroup$

Well, $sqrt[5]m$ is irrational if $m$ is an integer that isn't a perfect power of $5$.



And $sqrt[5]m$ is a solution to $x^5 -m =0$.



And as $x^5 -m =0implies x^5 = mimplies x =sqrt [5]m$ so that is the only solution.






share|cite|improve this answer









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    5 Answers
    5






    active

    oldest

    votes








    5 Answers
    5






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    4














    $begingroup$

    In fact we can even achieve this with a polynomial with rational coefficients: [Edit: After I wrote this answer, OP added the rationality of the coefficients as a condition.]



    The Rational Root Theorem implies that $$x^5 - 2$$ has no rational roots, but since its degree is odd, it has at least one real---and hence irrational---root. (In fact, can replace $2$ here with any rational number that is not a perfect $5$th power of a rational number.)






    share|cite|improve this answer











    $endgroup$










    • 1




      $begingroup$
      in fact with integer coefficients
      $endgroup$
      – J. W. Tanner
      10 hours ago






    • 1




      $begingroup$
      Indeed! That said, we can always clear the denominators of any rational polynomial by multiplying by their $operatornamelcm$, and this operation preserves the roots. (But it's true that this example is a monic polynomial with integer coefficients.)
      $endgroup$
      – Travis
      10 hours ago















    4














    $begingroup$

    In fact we can even achieve this with a polynomial with rational coefficients: [Edit: After I wrote this answer, OP added the rationality of the coefficients as a condition.]



    The Rational Root Theorem implies that $$x^5 - 2$$ has no rational roots, but since its degree is odd, it has at least one real---and hence irrational---root. (In fact, can replace $2$ here with any rational number that is not a perfect $5$th power of a rational number.)






    share|cite|improve this answer











    $endgroup$










    • 1




      $begingroup$
      in fact with integer coefficients
      $endgroup$
      – J. W. Tanner
      10 hours ago






    • 1




      $begingroup$
      Indeed! That said, we can always clear the denominators of any rational polynomial by multiplying by their $operatornamelcm$, and this operation preserves the roots. (But it's true that this example is a monic polynomial with integer coefficients.)
      $endgroup$
      – Travis
      10 hours ago













    4














    4










    4







    $begingroup$

    In fact we can even achieve this with a polynomial with rational coefficients: [Edit: After I wrote this answer, OP added the rationality of the coefficients as a condition.]



    The Rational Root Theorem implies that $$x^5 - 2$$ has no rational roots, but since its degree is odd, it has at least one real---and hence irrational---root. (In fact, can replace $2$ here with any rational number that is not a perfect $5$th power of a rational number.)






    share|cite|improve this answer











    $endgroup$



    In fact we can even achieve this with a polynomial with rational coefficients: [Edit: After I wrote this answer, OP added the rationality of the coefficients as a condition.]



    The Rational Root Theorem implies that $$x^5 - 2$$ has no rational roots, but since its degree is odd, it has at least one real---and hence irrational---root. (In fact, can replace $2$ here with any rational number that is not a perfect $5$th power of a rational number.)







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited 10 hours ago

























    answered 10 hours ago









    TravisTravis

    69.9k8 gold badges77 silver badges162 bronze badges




    69.9k8 gold badges77 silver badges162 bronze badges










    • 1




      $begingroup$
      in fact with integer coefficients
      $endgroup$
      – J. W. Tanner
      10 hours ago






    • 1




      $begingroup$
      Indeed! That said, we can always clear the denominators of any rational polynomial by multiplying by their $operatornamelcm$, and this operation preserves the roots. (But it's true that this example is a monic polynomial with integer coefficients.)
      $endgroup$
      – Travis
      10 hours ago












    • 1




      $begingroup$
      in fact with integer coefficients
      $endgroup$
      – J. W. Tanner
      10 hours ago






    • 1




      $begingroup$
      Indeed! That said, we can always clear the denominators of any rational polynomial by multiplying by their $operatornamelcm$, and this operation preserves the roots. (But it's true that this example is a monic polynomial with integer coefficients.)
      $endgroup$
      – Travis
      10 hours ago







    1




    1




    $begingroup$
    in fact with integer coefficients
    $endgroup$
    – J. W. Tanner
    10 hours ago




    $begingroup$
    in fact with integer coefficients
    $endgroup$
    – J. W. Tanner
    10 hours ago




    1




    1




    $begingroup$
    Indeed! That said, we can always clear the denominators of any rational polynomial by multiplying by their $operatornamelcm$, and this operation preserves the roots. (But it's true that this example is a monic polynomial with integer coefficients.)
    $endgroup$
    – Travis
    10 hours ago




    $begingroup$
    Indeed! That said, we can always clear the denominators of any rational polynomial by multiplying by their $operatornamelcm$, and this operation preserves the roots. (But it's true that this example is a monic polynomial with integer coefficients.)
    $endgroup$
    – Travis
    10 hours ago













    1














    $begingroup$

    That is pretty easy, if there are not other propertys required. Just consider a polynomial like:



    $(x-sqrt2)^5$






    share|cite|improve this answer









    $endgroup$














    • $begingroup$
      That doesn't have rational coefficients.
      $endgroup$
      – fleablood
      5 hours ago










    • $begingroup$
      @fleablood OP added the requirement that the coefficients be rational a few minutes after this answer was posted.
      $endgroup$
      – Travis
      3 hours ago















    1














    $begingroup$

    That is pretty easy, if there are not other propertys required. Just consider a polynomial like:



    $(x-sqrt2)^5$






    share|cite|improve this answer









    $endgroup$














    • $begingroup$
      That doesn't have rational coefficients.
      $endgroup$
      – fleablood
      5 hours ago










    • $begingroup$
      @fleablood OP added the requirement that the coefficients be rational a few minutes after this answer was posted.
      $endgroup$
      – Travis
      3 hours ago













    1














    1










    1







    $begingroup$

    That is pretty easy, if there are not other propertys required. Just consider a polynomial like:



    $(x-sqrt2)^5$






    share|cite|improve this answer









    $endgroup$



    That is pretty easy, if there are not other propertys required. Just consider a polynomial like:



    $(x-sqrt2)^5$







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered 10 hours ago









    CornmanCornman

    6,1612 gold badges13 silver badges33 bronze badges




    6,1612 gold badges13 silver badges33 bronze badges














    • $begingroup$
      That doesn't have rational coefficients.
      $endgroup$
      – fleablood
      5 hours ago










    • $begingroup$
      @fleablood OP added the requirement that the coefficients be rational a few minutes after this answer was posted.
      $endgroup$
      – Travis
      3 hours ago
















    • $begingroup$
      That doesn't have rational coefficients.
      $endgroup$
      – fleablood
      5 hours ago










    • $begingroup$
      @fleablood OP added the requirement that the coefficients be rational a few minutes after this answer was posted.
      $endgroup$
      – Travis
      3 hours ago















    $begingroup$
    That doesn't have rational coefficients.
    $endgroup$
    – fleablood
    5 hours ago




    $begingroup$
    That doesn't have rational coefficients.
    $endgroup$
    – fleablood
    5 hours ago












    $begingroup$
    @fleablood OP added the requirement that the coefficients be rational a few minutes after this answer was posted.
    $endgroup$
    – Travis
    3 hours ago




    $begingroup$
    @fleablood OP added the requirement that the coefficients be rational a few minutes after this answer was posted.
    $endgroup$
    – Travis
    3 hours ago











    1














    $begingroup$

    If $alpha$ is irrational, then the polynomial $(x-alpha)^5$ has degree $5$, and the only (repeated) root is irrational.






    share|cite|improve this answer









    $endgroup$










    • 2




      $begingroup$
      More generally, $(x-a_1)(x-a_2)(x-a_3)(x-a_4)(x-a_5)$ for any irrational $a_1, dots, a_5$.
      $endgroup$
      – 79037662
      10 hours ago










    • $begingroup$
      I realize now that I might have phrased the question badly- it is only considering polynomials with rational coefficients.
      $endgroup$
      – Diba
      10 hours ago






    • 1




      $begingroup$
      @DibaHeydary: In that case, see the answer by Travis
      $endgroup$
      – J. W. Tanner
      10 hours ago
















    1














    $begingroup$

    If $alpha$ is irrational, then the polynomial $(x-alpha)^5$ has degree $5$, and the only (repeated) root is irrational.






    share|cite|improve this answer









    $endgroup$










    • 2




      $begingroup$
      More generally, $(x-a_1)(x-a_2)(x-a_3)(x-a_4)(x-a_5)$ for any irrational $a_1, dots, a_5$.
      $endgroup$
      – 79037662
      10 hours ago










    • $begingroup$
      I realize now that I might have phrased the question badly- it is only considering polynomials with rational coefficients.
      $endgroup$
      – Diba
      10 hours ago






    • 1




      $begingroup$
      @DibaHeydary: In that case, see the answer by Travis
      $endgroup$
      – J. W. Tanner
      10 hours ago














    1














    1










    1







    $begingroup$

    If $alpha$ is irrational, then the polynomial $(x-alpha)^5$ has degree $5$, and the only (repeated) root is irrational.






    share|cite|improve this answer









    $endgroup$



    If $alpha$ is irrational, then the polynomial $(x-alpha)^5$ has degree $5$, and the only (repeated) root is irrational.







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered 10 hours ago









    J. W. TannerJ. W. Tanner

    16.9k1 gold badge12 silver badges35 bronze badges




    16.9k1 gold badge12 silver badges35 bronze badges










    • 2




      $begingroup$
      More generally, $(x-a_1)(x-a_2)(x-a_3)(x-a_4)(x-a_5)$ for any irrational $a_1, dots, a_5$.
      $endgroup$
      – 79037662
      10 hours ago










    • $begingroup$
      I realize now that I might have phrased the question badly- it is only considering polynomials with rational coefficients.
      $endgroup$
      – Diba
      10 hours ago






    • 1




      $begingroup$
      @DibaHeydary: In that case, see the answer by Travis
      $endgroup$
      – J. W. Tanner
      10 hours ago













    • 2




      $begingroup$
      More generally, $(x-a_1)(x-a_2)(x-a_3)(x-a_4)(x-a_5)$ for any irrational $a_1, dots, a_5$.
      $endgroup$
      – 79037662
      10 hours ago










    • $begingroup$
      I realize now that I might have phrased the question badly- it is only considering polynomials with rational coefficients.
      $endgroup$
      – Diba
      10 hours ago






    • 1




      $begingroup$
      @DibaHeydary: In that case, see the answer by Travis
      $endgroup$
      – J. W. Tanner
      10 hours ago








    2




    2




    $begingroup$
    More generally, $(x-a_1)(x-a_2)(x-a_3)(x-a_4)(x-a_5)$ for any irrational $a_1, dots, a_5$.
    $endgroup$
    – 79037662
    10 hours ago




    $begingroup$
    More generally, $(x-a_1)(x-a_2)(x-a_3)(x-a_4)(x-a_5)$ for any irrational $a_1, dots, a_5$.
    $endgroup$
    – 79037662
    10 hours ago












    $begingroup$
    I realize now that I might have phrased the question badly- it is only considering polynomials with rational coefficients.
    $endgroup$
    – Diba
    10 hours ago




    $begingroup$
    I realize now that I might have phrased the question badly- it is only considering polynomials with rational coefficients.
    $endgroup$
    – Diba
    10 hours ago




    1




    1




    $begingroup$
    @DibaHeydary: In that case, see the answer by Travis
    $endgroup$
    – J. W. Tanner
    10 hours ago





    $begingroup$
    @DibaHeydary: In that case, see the answer by Travis
    $endgroup$
    – J. W. Tanner
    10 hours ago












    1














    $begingroup$

    $$ x^5 + x^4 - 4 x^3 - 3 x^2 + 3 x + 1 $$



    Five real irrational roots,
    $$ 2 cos left( frac2k
    pi11 right) $$



    enter image description here



    If you prefer the roots to be $cos( 2k pi /11),$ adjust the quintic to



    $$ 32x^5 + 16x^4 - 32 x^3 - 12 x^2 + 6 x + 1 $$



    enter image description here



    gp-pari:



    ? x = cos( 2 * Pi / 11)
    %1 = 0.8412535328311811688618116489
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %2 = -1.009741959 E-28
    ?
    ? x = cos( 4 * Pi / 11)
    %3 = 0.4154150130018864255292741493
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %4 = -2.019483917 E-28
    ?
    ? x = cos( 6 * Pi / 11)
    %5 = -0.1423148382732851404437926686
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %6 = -7.57306469 E-29
    ?
    ? x = cos( 8 * Pi / 11)
    %7 = -0.6548607339452850640569250725
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %8 = 0.E-28
    ?


    =============================






    share|cite|improve this answer











    $endgroup$














    • $begingroup$
      I'm confused, how did you connect polynomials to triginometry? Through something like taylor series?
      $endgroup$
      – vikarjramun
      2 hours ago















    1














    $begingroup$

    $$ x^5 + x^4 - 4 x^3 - 3 x^2 + 3 x + 1 $$



    Five real irrational roots,
    $$ 2 cos left( frac2k
    pi11 right) $$



    enter image description here



    If you prefer the roots to be $cos( 2k pi /11),$ adjust the quintic to



    $$ 32x^5 + 16x^4 - 32 x^3 - 12 x^2 + 6 x + 1 $$



    enter image description here



    gp-pari:



    ? x = cos( 2 * Pi / 11)
    %1 = 0.8412535328311811688618116489
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %2 = -1.009741959 E-28
    ?
    ? x = cos( 4 * Pi / 11)
    %3 = 0.4154150130018864255292741493
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %4 = -2.019483917 E-28
    ?
    ? x = cos( 6 * Pi / 11)
    %5 = -0.1423148382732851404437926686
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %6 = -7.57306469 E-29
    ?
    ? x = cos( 8 * Pi / 11)
    %7 = -0.6548607339452850640569250725
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %8 = 0.E-28
    ?


    =============================






    share|cite|improve this answer











    $endgroup$














    • $begingroup$
      I'm confused, how did you connect polynomials to triginometry? Through something like taylor series?
      $endgroup$
      – vikarjramun
      2 hours ago













    1














    1










    1







    $begingroup$

    $$ x^5 + x^4 - 4 x^3 - 3 x^2 + 3 x + 1 $$



    Five real irrational roots,
    $$ 2 cos left( frac2k
    pi11 right) $$



    enter image description here



    If you prefer the roots to be $cos( 2k pi /11),$ adjust the quintic to



    $$ 32x^5 + 16x^4 - 32 x^3 - 12 x^2 + 6 x + 1 $$



    enter image description here



    gp-pari:



    ? x = cos( 2 * Pi / 11)
    %1 = 0.8412535328311811688618116489
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %2 = -1.009741959 E-28
    ?
    ? x = cos( 4 * Pi / 11)
    %3 = 0.4154150130018864255292741493
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %4 = -2.019483917 E-28
    ?
    ? x = cos( 6 * Pi / 11)
    %5 = -0.1423148382732851404437926686
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %6 = -7.57306469 E-29
    ?
    ? x = cos( 8 * Pi / 11)
    %7 = -0.6548607339452850640569250725
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %8 = 0.E-28
    ?


    =============================






    share|cite|improve this answer











    $endgroup$



    $$ x^5 + x^4 - 4 x^3 - 3 x^2 + 3 x + 1 $$



    Five real irrational roots,
    $$ 2 cos left( frac2k
    pi11 right) $$



    enter image description here



    If you prefer the roots to be $cos( 2k pi /11),$ adjust the quintic to



    $$ 32x^5 + 16x^4 - 32 x^3 - 12 x^2 + 6 x + 1 $$



    enter image description here



    gp-pari:



    ? x = cos( 2 * Pi / 11)
    %1 = 0.8412535328311811688618116489
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %2 = -1.009741959 E-28
    ?
    ? x = cos( 4 * Pi / 11)
    %3 = 0.4154150130018864255292741493
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %4 = -2.019483917 E-28
    ?
    ? x = cos( 6 * Pi / 11)
    %5 = -0.1423148382732851404437926686
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %6 = -7.57306469 E-29
    ?
    ? x = cos( 8 * Pi / 11)
    %7 = -0.6548607339452850640569250725
    ? f = 32 * x^5 + 16 * x^4 - 32 * x^3 - 12 * x^2 + 6 * x + 1
    %8 = 0.E-28
    ?


    =============================







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited 5 hours ago

























    answered 10 hours ago









    Will JagyWill Jagy

    109k5 gold badges107 silver badges209 bronze badges




    109k5 gold badges107 silver badges209 bronze badges














    • $begingroup$
      I'm confused, how did you connect polynomials to triginometry? Through something like taylor series?
      $endgroup$
      – vikarjramun
      2 hours ago
















    • $begingroup$
      I'm confused, how did you connect polynomials to triginometry? Through something like taylor series?
      $endgroup$
      – vikarjramun
      2 hours ago















    $begingroup$
    I'm confused, how did you connect polynomials to triginometry? Through something like taylor series?
    $endgroup$
    – vikarjramun
    2 hours ago




    $begingroup$
    I'm confused, how did you connect polynomials to triginometry? Through something like taylor series?
    $endgroup$
    – vikarjramun
    2 hours ago











    1














    $begingroup$

    Well, $sqrt[5]m$ is irrational if $m$ is an integer that isn't a perfect power of $5$.



    And $sqrt[5]m$ is a solution to $x^5 -m =0$.



    And as $x^5 -m =0implies x^5 = mimplies x =sqrt [5]m$ so that is the only solution.






    share|cite|improve this answer









    $endgroup$



















      1














      $begingroup$

      Well, $sqrt[5]m$ is irrational if $m$ is an integer that isn't a perfect power of $5$.



      And $sqrt[5]m$ is a solution to $x^5 -m =0$.



      And as $x^5 -m =0implies x^5 = mimplies x =sqrt [5]m$ so that is the only solution.






      share|cite|improve this answer









      $endgroup$

















        1














        1










        1







        $begingroup$

        Well, $sqrt[5]m$ is irrational if $m$ is an integer that isn't a perfect power of $5$.



        And $sqrt[5]m$ is a solution to $x^5 -m =0$.



        And as $x^5 -m =0implies x^5 = mimplies x =sqrt [5]m$ so that is the only solution.






        share|cite|improve this answer









        $endgroup$



        Well, $sqrt[5]m$ is irrational if $m$ is an integer that isn't a perfect power of $5$.



        And $sqrt[5]m$ is a solution to $x^5 -m =0$.



        And as $x^5 -m =0implies x^5 = mimplies x =sqrt [5]m$ so that is the only solution.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered 5 hours ago









        fleabloodfleablood

        81.3k2 gold badges32 silver badges99 bronze badges




        81.3k2 gold badges32 silver badges99 bronze badges































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