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Re: Integral giving complex answer

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59279] Re: Integral giving complex answer
  • From: mike_in_england2000 at yahoo.co.uk
  • Date: Thu, 4 Aug 2005 02:08:01 -0400 (EDT)
  • References: <dcples$6mm$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

David Sagan wrote:
> Hello:
>
> I am tring to do simple integrals but I am running into problems in that
> Mathematica gives the answer using complex numbers. For example,
> Integrate[1/(1 + 5x^2), x] gives a result in terms of logarithms of a
> complex argument instead of the usual arctan formula. If I integrate
> something like Integrate[1/(1 + a x^2), x] I get the answer in the form
> I want using the arctan.

Hi David
This probelm sounded interesting so I fired up Mathematica (I am using
version 5.1 btw) , copied and pasted your integration command and got

ArcTan[Sqrt[5]*x]/Sqrt[5]

as the result.  So i can't reproduce your problem.  Which version of
Mathematica are you using?  Do you get this problem on a clean, newly
opened notebook where the kernel has seen no previous calculations?

Mike


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