Portal:Geometry/Did you know

...that the hyperboloid of one sheet is a doubly ruled surface?
...that as the dimension of a hypersphere tends to infinity, its "volume" (content) tends to 0?
...that a nonconvex polygon with three convex vertices is called a pseudotriangle?
...that a regular heptagon is the regular polygon with the fewest number of sides which is not constructible with a compass and straightedge?
...that it is possible for a three dimensional figure to have a finite volume but infinite surface area? An example of this is Gabriel's Horn.