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MathGroup Archive 2003

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Re: differences in Solve with -1/2 and -0.5

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44396] Re: differences in Solve with -1/2 and -0.5
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sat, 8 Nov 2003 04:50:41 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <boftfo$5ph$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

the algorithm used by Solve[] divide by zero because it
does not see the common exponential factor. Help it with

Solve[Simplify[D[x E^(-0.5*x), x]] == 0, x]

Regards
  Jens

Kenneth Levasseur wrote:
> 
> Can anyone give a good reason why there is a difference in the
> following?  Preferably one that my students will understand.
> 
> In[1]:=
> Solve[D[x E^(-x/2), x] == 0, x]
> Out[1]=
> {{x -> 2}}
> In[2]:=
> Solve[D[x E^(-0.5*x), x] == 0, x]
> General::dbyz:Division by zero.
> Out[2]=
> {}
> 
> Ken Levasseur
> Math. Sciences
> UMass Lowell


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