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 90o. So their resultant is 2r. It acts mid-way between OC→ and OA→,i.e., along OB.Now, both r and 2r are along the same line and in the same directionResultant =r+2r=r(1+2)