Three forces F1,F2 and F3 are acting on a body and if this body is in equilibrium, then resultant of these three forces must be zero i.e. Fnet=F1+F2+F3=0 ⇒F1+F2=−F3 This situation can be shown graphically by three concurrent forces at 120° with each others. or, by three forces in the same order along three sides of a triangle.
Hence, both statement I and statement II are true.