The sum of these two vectors is the vector that begins at the origin of the first vector (the red one) and ends at the arrow head of the second (blue) vector. The sum of the two vectors is the vector ...The sum of these two vectors is the vector that begins at the origin of the first vector (the red one) and ends at the arrow head of the second (blue) vector. The sum of the two vectors is the vector that begins at the origin of the first vector and goes to the ending of the second vector, as shown below.