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MathGroup Archive 2000

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Re: Simplification shortcomings?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24666] Re: Simplification shortcomings?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 4 Aug 2000 01:18:54 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <8lsutf$27c@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

In[]:=FullSimplify[(1 + Sqrt[5])/2 - Sqrt[(3 + Sqrt[5])/2]]
Out[]=0

Regards
  Jens

Bob Harris wrote:
> 
> Howdy,
> 
> I'm a relative novice to Mathematica.  While working with it today, I had
> occasion to want to know if a result was equal to (1 + Sqrt[5])/2.  The
> result was shown as Sqrt[(3 + Sqrt[5])/2].  After some pancil and paper
> work, I figured out that these two are equal.  Or, I should say, that the
> former is one of the values that the latter can have.
> 
> I was frustrated in my attempts to get Mathematica to answer that question
> for me.  Simplify[(1 + Sqrt[5])/2 - Sqrt[(3 + Sqrt[5])/2]] didn't provide
> any improvement.  Calculating this value to many decimal digits showed it
> was near zero (probably close enough that I could have applied the
> techniques shown in Scheinerman's recent article in American Mathematical
> Monthly).  The only way I got Mathematica to show the equality was to square
> both numbers;  Simplify[((1 + Sqrt[5])/2)^2 - (3 + Sqrt[5])/2] is zero.
> 
> Is there any better way to do this?  I have some other, more complicated
> numbers that I need to compare.
> 
> Thanks,
> Bob Harris


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