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Re: Vertical Tangents

  • To: mathgroup at
  • Subject: [mg25831] Re: Vertical Tangents
  • From: "Allan Hayes" <hay at>
  • Date: Sat, 28 Oct 2000 01:41:23 -0400 (EDT)
  • References: <8t64dv$>
  • Sender: owner-wri-mathgroup at


You need to give ranges for both variables:

<< Graphics`ImplicitPlot`

ImplicitPlot[{x^2 + x*y + y^2 == 7, y == 2*Sqrt[7/3],
    x == 2*Sqrt[7/3]}, {x, -5, 5}, {y, -5, 5}]

Allan Hayes
Mathematica Training and Consulting
Leicester UK
hay at
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Tom Moriarty" <tjmor at> wrote in message
news:8t64dv$egv at
> 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?
> Let me tell you Mathematica certainly has helped my students (and me)
> visualize these implicit plots, without which they are just a matter of
> faith.
> Any help you can give me will be greatly appreciated.
> Tom Moriarty

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