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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: [mg44398] Re: [mg44386] differences in Solve with -1/2 and -0.5
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sat, 8 Nov 2003 04:50:43 -0500 (EST)
  • References: <200311071016.FAA05493@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 7 Nov 2003, at 19:16, 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
>
>
>

What version of Mathematica? In 5.0 I get:

In[4]:=
Solve[D[x E^(-x/2), x] == 0, x]

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

In[5]:=
Solve[D[x E^(-0.5*x), x] == 0, x]

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




Andrzej Kozlowski
Yokohama, Japan
http://www.mimuw.edu.pl/~akoz/


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