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MathGroup Archive 2005

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Re: exact integer from Log[ ]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58350] Re: exact integer from Log[ ]
  • From: Peter Pein <petsie at dordos.net>
  • Date: Tue, 28 Jun 2005 21:56:47 -0400 (EDT)
  • References: <d9r4o7$54g$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Trevor Baca schrieb:
> The question is how to get the exact integer 13 when we let
> 
>   f = 880*2^(1/12)
> 
> and let
> 
>   expr = Log[2^(1/12), f/440]
> 
> with no numerics (only exact integers) in both expressions.
> 
> It seems that expr should already equal the integer 13 exactly, yet
> evaluating expr gives
> 
>   (12*Log[2*2^(1/12)])/Log[2]
> 
> or
> 
>   Log[8192]/Log[2]
> 
> with Simplify[expr], which, while clearly 13 to the eye, still isn't
> exactgly 13 on the page.
> 
> So how do you get 13 back out of expr, preferably without recourse to
> numerics?
> 
> 
> Trevor.
> 

PowerExpand[expr]

-- 
Peter Pein
Berlin


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