A ruled surface formed by straight lines that are in turn supported on three straight lines that cross in space in pairs. We also get it when we consider straight lines between corresponding points of two parallel circumferences that have been rotated a certain angle between each other. The case of a revolution comes from rotating the two branches of a hyperbola around an axis of symmetry that does not cut them. The reduced equation is

Cones & spirals

Index

Hyperboloids of two sheets