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Re: Plot results not right

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90008] Re: Plot results not right
  • From: Narasimham <mathma18 at hotmail.com>
  • Date: Thu, 26 Jun 2008 04:43:04 -0400 (EDT)
  • References: <g3nhbc$g6$1@smc.vnet.net>

On Jun 23, 11:54 am, BrenB <GoogleGro... at ebesser.com> wrote:

> 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.

By cubing & simplifying or by Expand we can handle the troublesome
region x< 0.

Expand[(y - 4 - 2 x)^3 ] + 27 x^2

ContourPlot[% == 0, {x, -1, 6}, {y, -1, 6}, GridLines -> Automatic]

or

ContourPlot[-64 - 96 x - 21 x^2 - 8 x^3 + 48 y + 48 x y + 12 x^2 y -
12 y^2 - 6 x y^2 + y^3 == 0, {x, -1, 6}, {y, -1, 6}, GridLines ->
Automatic]

which gets the plot. At the cusp point (x,y) = (0,4) the curve slope
is indeterminate and curvature infinite.




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