Re: PowerExpand in mathematica

*To*: mathgroup at smc.vnet.net*Subject*: [mg31865] Re: [mg31843] PowerExpand in mathematica*From*: Andrzej Kozlowski <andrzej at tuins.ac.jp>*Date*: Sat, 8 Dec 2001 05:51:40 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Why is the correct answer -1/t (and why of course??). Mathematica quite correctly gives: In[24]:= Simplify[(-1/t)^(3/2) Sqrt[-t],t>0] Out[24]= 1 - t and In[25]:= Simplify[(-1/t)^(3/2) Sqrt[-t],t<0] Out[25]= 1 -(-) t PowerExpand makes certain assumptions about the variables and in this cases the assumption was that t is positive. You made the equally arbitrary assumption that t is negative. Why is your arbitrary assumption "obviously correct"? (Or have you not heard about complex numbers?) Andrzej Kozlowski Toyama International University JAPAN http://platon.c.u-tokyo.ac.jp/andrzej/ On Friday, December 7, 2001, at 07:56 PM, Peter wrote: > Hi, > > Is this a known bug, feature? Or I am doing something wrong? > ------------------------------- > Mathematica 4.0 for Linux > Copyright 1988-1999 Wolfram Research, Inc. > -- Motif graphics initialized -- > > In[1]:= PowerExpand[(-1/t)^(3/2) Sqrt[-t]] > > 1 > Out[1]= - > t > --------------------------------- > The correct answer is -1/t, of course. > > Thanks, > Peter > > >