Similarly, the tangent plane to a surface at a given point is the plane that "just touches" the surface at that point. The concept of a tangent is one of the most fundamental notions in [http://en.wikipedia.org/wiki/Differential_geometry differential geometry] and has been extensively generalized; | Similarly, the tangent plane to a surface at a given point is the plane that "just touches" the surface at that point. The concept of a tangent is one of the most fundamental notions in [http://en.wikipedia.org/wiki/Differential_geometry differential geometry] and has been extensively generalized; |