Re: exact integer from Log[ ]

*To*: mathgroup at smc.vnet.net*Subject*: [mg58337] Re: exact integer from Log[ ]*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Tue, 28 Jun 2005 21:56:37 -0400 (EDT)*Organization*: The Open University, Milton Keynes, England*References*: <d9r4o7$54g$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Trevor Baca wrote: > 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. > Hi Trevor, If I remember correctly, *Simplify* does very few attempt to manipulate exponents. So, try one of the following commands In[24]:= FullSimplify[expr] Out[24]= 13 In[25]:= PowerExpand[expr] Out[25]= 13 In[26]:= FunctionExpand[expr] Out[26]= 13 Best regards, /J.M.