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Re: Simplify results

  • To: mathgroup at smc.vnet.net
  • Subject: [mg118295] Re: Simplify results
  • From: Gary Wardall <gwardall at gmail.com>
  • Date: Wed, 20 Apr 2011 04:29:38 -0400 (EDT)
  • References: <iojpot$i4q$1@smc.vnet.net>

On Apr 19, 5:56 am, "Berthold Hamburger" <b-hambur... at artinso.com>
wrote:
> Hi,
>
> This might be a silly question, so please bear with me, but I have been
> scratching my head about it for some time now.
>
> Is there a particular reason why Mathematica (8.01) simplifies the following
> fraction reversing the signs in the result:
>
> IN:
>
> Simplify[(8a^2b^3(c^2+1)^4-6a^3b^2(c^2+1)^3+14a^4b
> (c^2+1)^2)/(4a^3b^2(c^2+1)^2-10a^4b^3(c^2+1)^3)]
>
> OUT:
>
> (-7 a^2+3 a b (1+c^2)-4 b^2 (1+c^2)^2)/(a b (-2+5 a b (1+c^2)))
>
> Reducing the fraction by hand gives me:
>
> (7 a^2-3 a b (1+c^2)+4 b^2 (1+c^2)^2)/(a b (2-5 a b (1+c^2)))
>
> Thanks
>
> Berthold
>
> --
>
> Berthold Hamburger - Cellist/Spain
>
> Email: beha... at artinso.com
>
> http://www.artinso.com
>
> http://www.astronomy.artinso.com

Berthold:

I got:

(-7 a^2 + 3 a b - 4 b^2 + 3 a b c^2 - 8 b^2 c^2 -
 4 b^2 c^4)/(-2 a b + 5 a^2 b^2 + 5 a^2 b^2 c^2)

by hand which is correct too, I think.

The point being there are many equivalent forms for mathematical
expressions. Mathematica would have to be clairvoyant to know which
form you would expect to expressions to simplify into.

Good Luck

Gary Wardall


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