Re: Re: Demostration

• To: mathgroup at smc.vnet.net
• Subject: [mg70465] Re: [mg70453] Re: [mg70369] Demostration
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Tue, 17 Oct 2006 02:58:32 -0400 (EDT)

The second test in Select is unnecessary. This should have been

Select[Flatten[
Table[{{x, -Sqrt[x^3 + 9]}, {x, Sqrt[x^3 + 9]}},
{x, -2, 500}], 1],
IntegerQ[#[[2]]] &]

Bob Hanlon

---- Bob Hanlon <hanlonr at cox.net> wrote:
> Reduce[{y^2==x^3+9}, {x,y},Integers]
>
> (x | y) Ã¢Ë?Ë? Integers && x >= -2 &&
>   (y == -Sqrt[x^3 + 9] || y == Sqrt[x^3 + 9])
>
> Select[Flatten[
>     Table[{{x,-Sqrt[x^3+9]},{x,Sqrt[x^3+9]}},
>       {x,-2,500}],1],
>   IntegerQ[#[[2]]]&&#[[2]]^2==#[[1]]^3+9&]
>
> {{-2, -1}, {-2, 1}, {0, -3}, {0, 3}, {3, -6}, {3, 6},
>   {6, -15}, {6, 15}, {40, -253}, {40, 253}}
>
> Length[%]
>
> 10
>
>
> Bob Hanlon
>
> ---- Miguel <mibelair at hotmail.com> wrote:
> > How canI to demostrate than the equation y^2=x^3+9 has 10 integer
> > solutions?
> >
>
> --
>
> Bob Hanlon
> hanlonr at cox.net
>
>

--

Bob Hanlon
hanlonr at cox.net

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