Vertical Tangents

*To*: mathgroup at smc.vnet.net*Subject*: [mg25787] Vertical Tangents*From*: Tom Moriarty <tjmor at erols.com>*Date*: Wed, 25 Oct 2000 03:53:45 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

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