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Re: Simplifying radicals

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122307] Re: Simplifying radicals
  • From: Dana DeLouis <dana01 at me.com>
  • Date: Mon, 24 Oct 2011 05:14:58 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

>  the principal cube root of a negative number will be complex ...
> Is there any EASY way I can simply ask for the cube root of -729 and get -9?

Hi.   Not the best way, but just to mention an alternative:

Power[-729., 1/3] 
4.5 +7.79423 I

Yep, it's complex like you mentioned.

The -Easy- way is to add the negative sign in front of the answer.

Power[-729., 1/3]  //Abs
9.

= = = = = = = = =
HTH
Dana DeLouis




On Oct 20, 7:49 am, Tom De Vries <tidetable... at gmail.com> wrote:

> Hi,  I'm working with some introductory topics in radicals.

> 

> I know that Mathematica assumes things about the domain used in

> problems,  so the principal cube root of a negative number will be

> complex... or something like that..

> 

> I'm way down at the lower high school level simply working with cube

> roots of negative numbers and wanting a negative number result.

> 

> I know there are ways of using assumptions and solving over the reals, etc.

> 

> Is there any EASY way I can simply ask for the cube root of -729 and get -9?

> 

> TOM


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