The triangle law of vectors states that if two vectors are represented in magnitude and direction by two sides of a triangle taken in order, then their resultant vector is represented in magnitude and direction by the third side of the triangle taken in the opposite order. This means that if we have two vectors A and B, and A + B is the resultant vector, then the tip of A can be placed at the tail of B, and the tip of B can be placed at the tail of A, forming a triangle whose closing side is the vector A + B.
