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MathGroup Archive 2001

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Re: System for which Solve and NSolve both fail

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30573] Re: System for which Solve and NSolve both fail
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Thu, 30 Aug 2001 03:51:20 -0400 (EDT)
  • References: <9mi1rt$54r$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Ben,
Both Solve and NSolve are primarilly for polynomial equations.
We can, of course, use

FindRoot[{3^x + 3^y == 90,x + y == 6},{x,1},{y,2}]

{x->2.,y->4.}

--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Ben Langton" <ben at spam.bugs.me.quickmath.com> wrote in message
news:9mi1rt$54r$1 at smc.vnet.net...
> Hi,
>
> I noticed that Mathematica seems unable to solve this system of equations
:
>
> 3^x + 3^y = 90
>
> x + y = 6
>
> With a bit of thought, you can see by inspection that the solutions are
>
> {x , y} = {2 , 4} or {4 , 2}
>
> However, when I use the commands
>
> Solve[{3^x+3^y==90,x+y==6},{x,y}]
>
> or
>
> NSolve[{3^x+3^y==90,x+y==6},{x,y}]
>
> I get a warning message starting with
>
> Solve::incnst: Inconsistent or redundant transcendental equation
>
> Can anyone shed some light on what is going on here? Any way to get around
> this problem?
>
> (I am using Mathematica v 3.0.0.0 under Mac OS 9.2.1, although I believe a
> similar thing occurs under v 4.x)
>
> Regards,
>
> Ben Langton
>
> http://www.quickmath.com/
>




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