The Parallelogram Rule:

Given two vectors, c and d, not equal to each other:

1. Place the initial points of both vectors in the same point and call it point O.

2. Draw a line parallel to vector c at the endpoint of vector d and also draw a line parallel to vector d at the endpoint of vector c, name the point of intersection of the parallel lines, call it point B.

3. `OB is the vector sum of vector c and vector d.