Meaning of parallelogram law

parallel'ogram law"

Pronunciation: [key]
  1. a rule for adding two vectors, as forcesby placing the point of application of one at the point of origin of the other and obtaining their sum by constructing the line connecting the two remaining end points, the sum being the diagonal of the parallelogram whose adjacent sides are the two vectors.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.