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Re: Reduce in Ver 6

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85484] Re: Reduce in Ver 6
  • From: Szabolcs <szhorvat at gmail.com>
  • Date: Mon, 11 Feb 2008 07:10:20 -0500 (EST)
  • References: <fopb8t$bkk$1@smc.vnet.net>

On Feb 11, 12:24 pm, "Dana DeLouis" <dana.... at gmail.com> wrote:
> Hi.  I was wondering if anyone knows of a more efficient way to do this.
> This issue came up in ver 6.0 with these equations:
>
> equ = {
> a + b + c == 3,
> a^2 + b^2 + c^2 < 10,
> a^3 + b^3 + c^3 == 15,
> a^4 + b^4 + c^4 == 35
>
> }
>
> I use Reduce, but 'c is returned as a function of a & b.
> What I would like is for c to replace a & b with the appropriate values.
>
> r = {ToRules[Reduce[equ, {a, b, c}]]}
>
> {{a -> 1, b -> 1 - Sqrt[2], c -> 3 - a - b},
>  {a -> 1, b -> 1 + Sqrt[2], c -> 3 - a - b},
>  {a -> 1 - Sqrt[2], b -> 1, c -> 3 - a - b},
>  {a -> 1 - Sqrt[2], b -> 1 + Sqrt[2], c -> 3 - a - b},
>  {a -> 1 + Sqrt[2], b -> 1, c -> 3 - a - b},
>  {a -> 1 + Sqrt[2], b -> 1 - Sqrt[2], c -> 3 - a - b}}
>

Hi,

Use the Backsubstitution -> True setting for Reduce[]

Szabolcs


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