In mathematics, an invariant is a property of a mathematical object (or a class of mathematical objects) which remains unchanged after operations or transformations of a certain type are applied to the objects. The particular class of objects and type of transformations are usually indicated by the context in which the term is used. For example, the area of a triangle is an invariant with ...

Equiareal map; Heronian triangle, a triangle with integer sides and integer area. List of triangle inequalities; One-seventh area triangle, an inner triangle with one-seventh the area of the reference triangle. Routh's theorem, a generalization of the one-seventh area triangle. Orders of magnitude—A list of areas by size.