7.All forces do not lie in the same plane and their lines of action do not pass through a single point.This is the most general case and both the conditions of eqn.(2.1) need to be checked.

Equation of equilibrium

	5. Non coplanar parallel forces: In this case, all the forces are parallel to each other, but not in the same plane. An example is forces on the table, when a book is kept on it. Here, both the conditions have to be checked.	6. Non-coplanar concurrent forces: In this system, all forces do not lie in the same plane, but their line of action passes through a single point. For example, if a disc of weight W is suspended by means of three strings, line of action of all the forces pass through point O. The forces do not lie in a plane. The second condition of equation(2.1) is automatically satisfied. For equilibrium the first condition is to be checked.