A structure which can not be solved by applying the conditions of static equilibrium is known as indeterminate structures.

$?.$ The influence line of a determinate structure all consist of straight line segments.

In the case of a multi$-$span determinate beam with forces in the subsidiary parts, only the subsidiary parts produce internal forces.

Three rigid bodies joined pairwise by hinges, provided that the three hinges do not lie on the same straight line, will form an internally stable system without redundant restraints

$$ i$.$ The primary system in force method is not necessarily determinate one.