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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: [mg30575] Re: [mg30572] System for which Solve and NSolve both fail
  • From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
  • Date: Thu, 30 Aug 2001 03:51:21 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

The brief answer is: a bit of thought is far to much to expect of a 
computer program. General algorithms for solving equations used by Solve 
and NSolve work only for algebraic equations, hence the message you are 
getting. The "way round this problem is" either

1. A bit of thought and inspection

or

2.

In[5]:=
FindRoot[{3^x + 3^y == 90,x+y==6},{x,1},{y,1}]

Out[5]=
{x -> 4., y -> 2.}

Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/

On Wednesday, August 29, 2001, at 02:40  PM, 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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