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Re: Beginner--How to get a positive solution from Solve Command

• To: mathgroup at smc.vnet.net
• Subject: [mg67812] Re: Beginner--How to get a positive solution from Solve Command
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Sat, 8 Jul 2006 04:56:44 -0400 (EDT)
• References: <e8lgq7$ras$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

Assuming[{c >= 0 && c <= 1},
   f = Normal[Series[1 - c*ArcTan[x]/x, {x, 0, 2}]];
   lst = x /. Solve[f == 0, x] // FullSimplify;
   Select[lst, ! MatchQ[#, -1*_] &]
   ]

Regards
   Jens

abdou.oumaima at hotmail.com wrote:
> Hello mathgroup,
> 
> I'm trying to solve and equation in a limit case, so I've to use Taylor series.
> 
> In[1]: Normal[Series[1 - c  ArcTanh[&#958;]/&#958;, {&#958;, 0, 2}]]
> Out[1]: 1-c-c (&#958;^2/3)
> 
> and 
> 
> In[2]: Solve[%==0,&#958;]
> Out[2]: {{&#958;->- (3(1-c)/&#958;)^1/2},{&#958;->(3(1-c)/&#958;)^1/2}}
> 
> I need just the positive solution. How to force Solve to give me the positive value please.
> 
> Any Help please.
> 
> Thank you
> 
> Link to the forum page for this post:
> http://www.mathematica-users.org/webMathematica/wiki/wiki.jsp?pageName=Special:Forum_ViewTopic&pid=11752#p11752
> Posted through http://www.mathematica-users.org [[postId=11752]]
> 
>