Hey,
example similar to: http://tutorial.math.lamar.edu/Classes/CalcIII/ParametricSurfaces.aspx
Afterwards, its the same process I went thru above with the cone
Hey, dunno if I understand completely but here is what I think (btw I am still getting used to using the latex math symbols here so I won't use them in this response)
Use the cross product (copied&pasted this one):
Here the vector is normal to the circle's surface in the positive Z...