Write the condition for equilibrium when two forces act on a particle.

(N/A) For a particle to be in equilibrium under the action of two forces,the net force acting on the particle must be zero.
Let the two forces be $\vec{F}_1$ and $\vec{F}_2$.
The condition for equilibrium is $\vec{F}_1 + \vec{F}_2 = 0$.
This implies $\vec{F}_1 = -\vec{F}_2$.
Therefore,the two forces must be equal in magnitude,opposite in direction,and must act along the same line of action.