We have two vectors: V1 and V2 (blue colors).
The vector sum V3 = V1 + V2 (red color) of these two vectors is given by:
V3 = [V3x,V3y] = [V1x,V1y] + [V2x,V2y] = [V1x+V2x,V1y+V2y]
The default values of these vectors are:
V3 = [V3x,V3y] = [V1x,V1y] + [V2x,V2y]
= [2,1] + [1,3]
= [2+1,1+3]
= [3,4]
Drag the end points of the vectors V1 and V2 and observe the vector sum V3.