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Re: Inverse function warnings

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99174] Re: Inverse function warnings
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 29 Apr 2009 06:05:59 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <gt90og$l55$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

because

Table[3^(2 x) - 12 (3^x) + 27 == 0 /.
   x -> 1 + 2 I*Pi*any/Log[3], {any, 1, 10}]

gives True for all any and this is only found by Reduce[]
and not by Solve[].

Use

Quiet[
  Solve[3^(2 x) - 12 (3^x) + 27 == 0, x]
  ]

if you wish to ignore an infinite number of solutions.

Regards
   Jens


davef wrote:
> When I execute this in Mathematica 7:
> 
> Solve[3^(2 x) - 12 (3^x) + 27 == 0, x]
> 
> I get this:
> 
> Solve::ifun: Inverse functions are being used by Solve, so some solutions may not be found; use Reduce for complete solution information. >> 
> 
> {{x->1},{x->2}}
> 
> 
> 1 amd 2 are proper solutions but is it possible to avoid the warning?
> 
> If I use Reduce:
> 
> Reduce[3^(2 x) - 12 (3^x) + 27 == 0, x]
> 
> I get a set of 1 and 2 added to some imaginary number terms that I don't quite understand.
> 
> I guess my question is: why would the use of inverse functions be so unreliable a solution as to necessitate a warning?  And in the interest of clean output, can the warning be supressed other than by deleteing the cell?  
> 
> Thanks
> 


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