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Re: Integral giving complex answer

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59323] Re: Integral giving complex answer
  • From: "Scout" <not at nothing.net>
  • Date: Fri, 5 Aug 2005 01:22:59 -0400 (EDT)
  • References: <dcples$6mm$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

> 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.
>
> My question is how to avoid getting the answer to Integrate[1/(1 +
> 5x^2), x] in terms of complex logarithms. I know I could just integrate
> 1/(1 + a x^2) and substitute a -> 5 later but in actuality I am dealing
> with more complex integrals and it would be helpful if I did not have to
> be making such substitutions.
>
>            -- Thanks for any help, David Sagan
>

In[1]:= $Version
Out[1]= 4.0 for Microsoft Windows (April 21, 1999)

In[2]:= Integrate[1/(1 + 5x^2), x]
Out[2]= ArcTan[Sqrt[5] x] / Sqrt[5]

Regards,
    ~Scout~ 


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