Re: Is -1^(2/5) really undefined in R?

*To*: mathgroup at smc.vnet.net*Subject*: [mg69102] Re: Is -1^(2/5) really undefined in R?*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Wed, 30 Aug 2006 06:33:05 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <ed0uvq$po$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Ben wrote: > Is -1^(2/5) really undefined in R? Yes. > Mathematica seems to think so, I guess since it looks like a negative square root, but > > -1^(2/5) = (-1^2)^(1/5) = 1^(1/5) = 1 > > Is this correct mathematically? No. See "College Algebra Tutorial 5: Rational Exponents" at http://www.wtamu.edu/academic/anns/mps/math/mathlab/col_algebra/col_alg_tut5_ratexp.htm In[12]:= ((-1)^(1/5))^2 Out[12]= 2/5 (-1) In[13]:= (-1)^(2/5)==((-1)^(1/5))^2 Out[13]= True (-1)^(2/5)==((-1)^2)^(1/5) Out[14]= False HTH, Jean-Marc