       Re: Trinomial decics x^10+ax+b = 0; Help with Mathematica code

• To: mathgroup at smc.vnet.net
• Subject: [mg93298] Re: [mg93280] Trinomial decics x^10+ax+b = 0; Help with Mathematica code
• From: "Tito Piezas" <tpiezas at gmail.com>
• Date: Mon, 3 Nov 2008 05:26:27 -0500 (EST)
• References: <200811020657.BAA02645@smc.vnet.net>

```Hello Bob,

There is no non-trivial solution with {a,|b|} < 100?  That is strange.

There are an *infinite* number of solutions such that an irreducible
x^6+ax+b or x^8+ax+b factors over a Sqrt[] extension.

A non-trivial soln {a,b} such that the 45-deg resultant has a 10th deg (or
5th deg) factor would mean that x^10+ax+b factors over a Sqrt (or a quintic)
extension.

I will extend the range to {a,|b|} < 1000 tomorrow when I have time.

Lots of thanks.  :-)

Tito

On Sun, Nov 2, 2008 at 12:45 PM, Bob Hanlon <hanlonr at cox.net> wrote:

> eqns = {-a + m^9 - 8 m^7 n + 21 m^5 n^2 - 20 m^3 n^3 + 5 m n^4 == 0,
>   -b + m^8 n - 7 m^6 n^2 + 15 m^4 n^3 - 10 m^2 n^4 + n^5 == 0};
>
> R[m_, a_, b_] = Resultant[Sequence @@ First /@ eqns, n]
>
> m^45+246 a m^36-502 b m^35-13606 a^2 m^27+51954 a b m^26-73749 b^2 m^25-245
> \
> a^3 m^18+135060 a^2 b m^17-92850 a b^2 m^16+383750 b^3 m^15+13605 a^4 \
> m^9+27200 a^3 b m^8+25125 a^2 b^2 m^7+12500 a b^3 m^6+3125 b^4 m^5-a^5
>
> For a = 0 and b != 0 there will always be a quintic factor
>
> {R[m, 0, 0], R[m, 0, b]} // Factor
>
> {m^45,m^5 (m^20-625 b m^10+3125 b^2) (m^20+123 b m^10+b^2)}
>
> To test factored polynomials for factors of a specific degree
>
> Clear[FactorQ];
>
> FactorQ[factoredPoly_Times, deg_Integer, m_Symbol] :=
>
>  Or @@ (FactorQ[#, deg, m] & /@ (List @@ factoredPoly));
>
> FactorQ[factoredPoly_Power, deg_Integer, m_Symbol] :=
>
>  If[factoredPoly === m^deg, True, FactorQ[factoredPoly[], deg, m]];
>
> FactorQ[factoredPoly_, deg_Integer,
>   m_Symbol] :=
>  (Length[CoefficientList[factoredPoly, m]] - 1) == deg;
>
> FactorQ[#, 2, x] & /@
>  {(x + 1) (x + 2), (x + 1)^2 (x + 2), x^2, (x + 1)^2,
>  x^2 + 1, (x^2 + 1) (x + 2), (x^2 + 1)^3 (x + 2)}
>
> {False,False,True,False,True,True,True}
>
> polys1 = Flatten[
>   Table[{a, b, Factor[R[m, a, b]]}, {a, -100, -1}, {b, -100, 100}], 1];
>
> ans1 = Select[polys1, FactorQ[#[], 5, m] || FactorQ[#[], 10, m] &]
>
> {}
>
> polys2 = Flatten[
>   Table[{a, b, Factor[R[m, a, b]]}, {a, 1, 100}, {b, -100, 100}], 1];
>
> ans2 = Select[polys2, FactorQ[#[], 5, m] || FactorQ[#[], 10, m] &]
>
> {}
>
> Not too encouraging for finding other cases.
>
>
> Bob Hanlon
>
> ---- tpiezas at gmail.com wrote:
>
> =============
> Hello guys,
>
> I need some help with Mathematica code.
>
> It is easy to eliminate "n" between the two eqn:
>
> -a + m^9 - 8m^7n + 21m^5n^2 - 20m^3n^3 + 5mn^4 = 0
> -b + m^8n - 7m^6n^2 + 15m^4n^3 - 10m^2n^4 + n^5 = 0
>
> using the Resultant[] command to find the rather simple 45-deg
> polynomial in "m", call it R(m).
>
> As Mathematica runs through integral values of {a,b}, if for some
> {a,b} the poly R(m) factors, we are interested in two cases:
>
> Case1: an irreducible decic factor
> Case2: an irreducible quintic factor
>
> What is the Mathematica code that tells us what {a,b} gives Case 1 or
> Case 2?
>
>
> Thanks.  :-)
>
>
> Tito
>
>
>
>
> --
>
> Bob Hanlon
>
>

```

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