Polygon Law of Forces:
If any number of forces acting on a particle are represented in magnitude and direction by the sides of a polygon, taken in order, then the forces will be in equilibrium.
Proof: Let the forces P, Q, R, S, T, and U acting at a point O be represented in magnitude and direction by the sides AB, BC, CD, DE, EF, and FA of a polygon ABCDEF.
Hence the forces are in equilibrium.
Note: The converse of the polygon law of forces does not hold good because polygons with their corresponding sides parallel may not have their corresponding sides proportional.