Consider an object on which multiple forces act. When the lines of action of these forces lie within the same plane, the system is known as a coplanar force system. All these forces can be resolved into their respective components using cartesian vector form. A coplanar system will be in equilibrium if each component of the resultant force equals zero and the resultant force on the system is zero. These are called equations of equilibrium for a coplanar force system. Consider a box in equilibrium held by three strings. The system is said to be a coplanar force system because the forces act in a single plane. Two strings make an angle Theta with the plank. The tension force in these two strings is known. The magnitude of the tension force in the third string can be determined by applying the equilibrium equations. Resolving the known tension forces into its components show that the horizontal components counterbalance each other. Now, the tension in the third string can be determined by rearranging the equation for vertical components.