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MathGroup Archive 2004

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Re: Forcing functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51027] Re: [mg51006] Forcing functions
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sat, 2 Oct 2004 03:17:55 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 1 Oct 2004, at 17:48, Barry Tesman wrote:

> Can you "force" Mathematica to not use certain functions?  E.g., I
> want to give my students some problems to antidifferentiate.  One
> such problem is:
>
> Integrate[ x * Sqrt[x^2 + 2x +4], x]
>
> The answer uses arcsinh.  Can one force Mathematica to use natural
> log instead?
>
> Thanks,
> Barry
>
The answer is not really , but....

If you evaluate at the begining of a session:

$Post = (If[! FreeQ[#, ArcSinh | ArcCosh], TrigToExp[#], #] &);


then



Integrate[x*Sqrt[x^2+2x+4],x]


(1/6)*(Sqrt[x^2 + 2*x + 4]*(2*x^2 + x + 5) - 9*Log[(x + 1)/Sqrt[3] + 
Sqrt[(1/3)*(x + 1)^2 + 1]])

You could even put this definiton into an init.m file so that it is 
evaluated every time Mathematica is run.



Andrzej Kozlowski
Chiba, Japan
http://www.akikoz.net/~andrzej/
http://www.mimuw.edu.pl/~akoz/


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