Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

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


  • Prev by Date: Interpretation should accept SelectWithContents
  • Next by Date: Re: Cube root of -1 and 1
  • Previous by thread: Re: Cube root of -1 and 1
  • Next by thread: Re: Cube root of -1 and 1