The resultant of the three vectors OA→, OB→, and OC→ shown in figure is

OC→ and OA→ are equal in magnitude and inclined to each other at an angle of 90∘ So their resultant is 2r. It acts midway between OC→ and OA→, i.e., along OB.Now, both r and 2r are along the same line and in the same direction.  Resultant =r+2r=r(1+2)