Resultant force is the total force acting on a body including their directions. If the object is at rest or it moves with a same velocity, the resultant force should be zero. All forces are acting on the same direction, resultant force should be the sum of all the forces. One force is acting perpendicular to other, resultant force can be calculated by using Pythagorean theorem. If the force F1,F2 and F3 are acting on a body in same direction. So the formula for resultant force is,
Resultant Force