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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: [mg30585] Re: System for which Solve and NSolve both fail
  • From: David Reiss <dreissNOSPAM at DELETEscientificREMOVEMEarts.com>
  • Date: Thu, 30 Aug 2001 03:51:31 -0400 (EDT)
  • Organization: Scientific Arts
  • References: <9mi1rt$54r$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Of course this is the same as :

In[1]:=
Solve[{3^x+3^(6-x) == 90},{x}]

Out[1]=
{{x -> 2},{x -> 4}}

Which are your solutions...

--David

Ben Langton wrote:

> 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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