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Re: Vertical Tangents

  • To: mathgroup at
  • Subject: [mg25806] Re: Vertical Tangents
  • From: Albert Retey <albert.retey at>
  • Date: Sat, 28 Oct 2000 01:41:00 -0400 (EDT)
  • Organization: Visual Analysis
  • References: <8t64dv$>
  • Sender: owner-wri-mathgroup at

Tom Moriarty wrote:
> This group was very helpful on my last question and I hope you will be
> willing to once again come to the aid of a teacher trying to illustrate
> to calculus students tangents to implicit plots.  By the way, I
> purchased Mathematica on my own, it is not available to me at school -
> so I plot at home and Xerox handouts for the kids.  I have been able to
> show them various implicit plots and tangents to them - for example
> ImplicitPlot[{x^2 + x*y + y^2==7, y == 2*Sqrt[7/3]},{x,-5,5}] which
> clearly shows the ellipse and one of the horizontal tangents (as asked
> for in the textbook problem).  But the problem also asked for the
> vertical tangents, one of which would be x == 2*Sqrt[7/3], but I get the
> message that this equation does not have a single variable other than
> x.  Is there any way to plot a vertical line?

I don't have expericence with ImplicitPlot, so I don't know whether you
can make it plot what you need, but a simple way to produce a vertical
line is:

p = ParametricPlot[{2*Sqrt[7/3], t}, {t, -10, 10}]

Then use Show to put it together with your ImplicitPlots


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