Re: Cube root of -1 and 1
- To: mathgroup at smc.vnet.net
- Subject: [mg90881] Re: Cube root of -1 and 1
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Mon, 28 Jul 2008 07:51:30 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <g6h5fm$h26$1@smc.vnet.net>
Bob F wrote: > Could someone explain why Mathematica evaluates these so differently? > > In[53]:= > > (Sqrt[36] - 7)^(1/3) > (Sqrt[36] - 5)^(1/3) > > Out[53]= (-1)^(1/3) > > Out[54]= 1 > > In other words why isn't (-1)^1/3 expressed as -1 ?? Branch cut and principal root are the key words here. See, "How do I get x^(1/3) (where x is a negative number) to evaluate to a real number?" http://support.wolfram.com/mathematica/mathematics/algebra/realpower.html Regards, -- Jean-Marc