# Why does the sss postulate work?

##### 1 Answer

According to a universally accepted system of axioms of Geometry developed by Hilbert, only side-angle-side (SAS) is an axiom.

Two others, ASA and SSS are theorems requiring proofs.

#### Explanation:

Strictly speaking, side-side-side (SSS) congruence of triangles, as well as angle-side-angle (ASA) are theorems (statements we should prove).

Only side-angle-side (SAS) is accepted in the Hilbert system as an axiom.

*Postulates* and *axioms* are equivalent terms and mean the same - they are the statements that we accept without proof.

IMPORTANT: they are not "obvious" statements and not statements that "do not require the proof". We just have to accept them to build a hierarchy of logical conclusions upon them because we have to have some statements in the foundation.

Full description of axiomatic approach to Geometry and proofs of angle-side-angle (ASA) and side-side-side (SSS) theorems about congruence of triangles can be found at Unizor by following the menu items *Geometry - Triangles - Congruence*.