       Re: Solve bug !!

• To: mathgroup at smc.vnet.net
• Subject: [mg31211] Re: Solve bug !!
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 19 Oct 2001 03:12:01 -0400 (EDT)
• Organization: Universitaet Leipzig
• References: <9qjjlh\$j84\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,

why we *must* obtain a minus sign ?

In[]:=
eqn = (E^(-c))^2 - A*E^(-c) + 1 == 0;
sol = Solve[eqn, c];
sol = Solve[eqn, c]
Out[]={True,True}

especial if you get a message like

Solve::"ifun": "Inverse functions are being used by \!\(Solve\), so some
\
solutions may not be found."

Regards
Jens

Marcel wrote:
>
> Where is the minus sign whe must obtain in the second case??
>
> > Solve[(E^c)^2 - A*E^c + 1 == 0, c]
>
> {{c -> Log[(1/2)*(A - Sqrt[-4 + A^2])]},
>   {c -> Log[(1/2)*(A + Sqrt[-4 + A^2])]}}
>
> > Solve[(E^(-c))^2 - A*E^(-c) + 1 == 0, c]
>
> {{c -> Log[(1/2)*(A - Sqrt[-4 + A^2])]},
>   {c -> Log[(1/2)*(A + Sqrt[-4 + A^2])]}}
>
> Mathematica 4.1, Windows 2000 SP2, PII400.
>
> Marcel Aguilella

```

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