Re: Simplifying radicals
- To: mathgroup at smc.vnet.net
- Subject: [mg122211] Re: Simplifying radicals
- From: "Oleksandr Rasputinov" <oleksandr_rasputinov at hmamail.com>
- Date: Fri, 21 Oct 2011 06:22:27 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <j7p1s8$5ko$1@smc.vnet.net>
On Thu, 20 Oct 2011 12:49:28 +0100, Tom De Vries <tidetabletom 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 > negativeCubeRoot[num_?Negative] := Block[{x}, x /. ToRules@Reduce[num == x^3 && x < 0, x, Reals] ]; negativeCubeRoot[-729] -9 negativeCubeRoot[-150] -5^(2/3) 6^(1/3) negativeCubeRoot[-73.8] -4.19455