In the two hinge arch, we have 2 hinges at two support of the arch and have four reaction components, as in a 3 hinge arch.

Degree of static indeterminancy = no of reactions- no of equilibrium equations= 4 − 3 = 1: statically

But here we don't have an additional equation to solve the structure and hence our 2 hinge arch is indeterminate by degree 1.

For a cantilever beam,

Degree of static indeterminancy = no of reactions- no of equilibrium equations= 3 − 3=0: statically determinate

For the three-hinged arch,

Degree of static indeterminancy = no of reactions- no of equilibrium equations= 3 − 3=0: statically determinate

For simply supported beams,

Degree of static indeterminancy = no of reactions- no of equilibrium equations= 3 − 3=0: statically determinate