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Re: Plot results not right

  • To: mathgroup at smc.vnet.net
  • Subject: [mg89889] Re: Plot results not right
  • From: "David W.Cantrell" <DWCantrell at sigmaxi.net>
  • Date: Tue, 24 Jun 2008 03:25:25 -0400 (EDT)
  • References: <g3nhbc$g6$1@smc.vnet.net>

BrenB <GoogleGroups at ebesser.com> wrote:
> I'm new to Mathematica.
>
> I'm studying Calculus, and I'm trying to reproduce, in Mathematica,
> the graph results of an equation in my book.
>
> Plot[2 x - 3 x^(2/3) + 4, {x, -1, 6}]
>
> The output graph is correct, except there should be graphing in the
> 2nd and 3rd quadrant, and there is none.
>
> Is there another way to enter this equation into Mathematica to get
> the correct graph results?

Yes:

Plot[2 x - 3 (x^2)^(1/3) + 4, {x, -1, 6}]

Note that, for negative x, x^(2/3) and (x^2)^(1/3) are not the same in
Mathematica. The latter expression gives a positive value, which is what
you want, while the former expression gives the _principal_ value of the
2/3 power, which has a nonzero imaginary part and so does not plot.

David


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