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Re: The graph of (x + 2)^(1/5) + 4 not plotted correctly

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  • Subject: [mg103962] Re: The graph of (x + 2)^(1/5) + 4 not plotted correctly
  • From: Mike Bryniarski <melondisco at gmail.com>
  • Date: Tue, 13 Oct 2009 23:22:33 -0400 (EDT)
  • References: <868306d90910120643u7f1c2299v2cd1845508dc85b7@mail.gmail.com>

The link you posted does not seem to relate to your problem. you
wanted to show :

Plot[ (x + 2)^(1/5) + 4 , {x, -4, 4}]

I tried plotting the function in your subject and not surprisingly it
did not plot correctly.
the issue is taking the fifth root of x on Mathematica can result in a
complex number. (This can bee seen under possible issues on the Power
page in the documentation)
Example:

in: (x + 2)^(1/5) + 4 /. x -> -3

out: 4 + (-1)^(1/5)

The most obvious way (at least for me) to overcome this is to perform
some algebra on the function to eliminate the fractional power and
plot it in ContourPlot instead:

ContourPlot[(y - 4)^5 == x + 2, {x, -4, 4}, {y, 0, 6}]

This is the result I assume you were looking for.

On Oct 13, 7:22 am, victor chg <kindlych... at gmail.com> wrote:
> Here is the link to the image:http://tinypic.com/view.php?pic=veae6u&s=
=4
>
> Victor Chg
> --------------------------------------
> Neuroscience Research Institute, Peking University, Beijing, P.R.China
> 100038



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