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MathGroup Archive 1999

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Re: New user question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg20394] Re: [mg20383] New user question
  • From: BobHanlon at aol.com
  • Date: Tue, 26 Oct 1999 00:32:50 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Solve[y^3 == -4, y] // N

{{y -> 0.7937005259840992 - 1.3747296369986026*I}, 
  {y -> -1.5874010519681991}, 
  {y -> 0.7937005259840998 + 1.3747296369986022*I}}

For a negative argument, the default cube root is complex

N[(-4)^(1/3)]

0.7937005259840998 + 1.3747296369986022*I

Since you are only interested in the real root

Plot[Sign[x] * Abs[x^(1/3)], {x, -5, 5}];

Bob Hanlon

In a message dated 10/18/1999 5:28:30 AM, moriarty at umd5.umd.edu writes:

>I have just begun to use/learn Mathematica.  One of the first things I
>tried was to Plot[x^(1/3),{x,-5,5}] and got error messages indicating that
>the negatives^(1/3) were not machine level real numbers (or close to
>that) - the positive side displayed ok.
>


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