If a rigid body is in equilibrium under the action of three forces, then

Question

RRB Paper · Accepted Answer

If a rigid body is in equilibrium under the action of only three forces, these forces must be either concurrent or parallel.

If a body in equilibrium is acted upon by three forces, then the resultant of any two forces must be equal, opposite, and collinear with the third force.
If a three-force member is in equilibrium and the forces are not parallel, they must be concurrent.
Therefore, the lines of action of all three forces acting on such a member must intersect at a common point; any single force is, therefore, the equilibrant of the other two forces.

If it does not pass through a common point, it will produce a couple.

These forces are equal