Answer: The resultant force = Zero(0)
Explanation: resolving the vector into X and Y component
AB = A
BC = -A cos60 + A sin60
= - A/2 + 0.866A
CA = - A cos60 - A sin 60
= -A/2 - 0.866A
Sum of the magnitude in the X component
A - A/2 - A/2 = 0
Sum of the magnitude in the Y component
- 0.866A + 0.866A = 0
Resultant vector = root(X^2 + Y^2) = 0
Therefore
AB + BC + CA = 0