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MathGroup Archive 2005

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Re: Please explain this weird Integrate result

  • To: mathgroup at smc.vnet.net
  • Subject: [mg60142] Re: Please explain this weird Integrate result
  • From: "Scout" <not at nothing.net>
  • Date: Sun, 4 Sep 2005 03:02:05 -0400 (EDT)
  • References: <dfbevv$inu$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Jose Reckoner" <reckoner at gmail.com>
>
> Expand[Integrate[(2*x)/(2*x - 1), x]]
>
> gives
>
> -1/2 + x + Log[-1 + 2*x]/2
>
> But,
>
> Expand[Integrate[1 + 1/(-1 + 2*x), x]]
>
> gives
>
> x + Log[-1 + 2*x]/2
>
> even though
>
> (2*x)/(2*x - 1) == 1 + 1/(-1 + 2*x)
>
> Where did the extra -1/2 in the first result come from?
>
Hi Jose,
I don't know why you've obtained these different (and incorrect) results on 
the same integral!
Maybe some pre-assignements on x? (Clear[] will help you ;-) )
 On my system (Math.4) it gives:

    In[1]:= a=Expand[Integrate[(2*x)/(2*x - 1), x]];
    In[2]:= b=Expand[Integrate[1 + 1/(-1 + 2*x), x]];
    In[3]:= a==b
    Out[3]= True
    In[4]:= a
    Out[4]= x + Log[-1+2 x] / 2


 ~Scout~


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