Two vectors in the opposite direction of each other gives the smallest resultant, where as two vector in the same direction gives the largest resultant.
Smallest Resultant: when two vectors, acts in opposite direction (180°) to each other, the resultant of these vector is simply the subtraction of both the vectors, having the direction of largest magnitude vector.
Largest resultant: when two vectors, acts in same direction (0°) to each other, the resultant of these vector is simply the addition of both the vectors, having the same direction as the forming vectors.