Final answer:
Triangles are congruent by SSS when all three sides of one triangle are equal to the corresponding sides of another triangle. Verifying that all corresponding sides have the same length according to the SSS postulate confirms congruency.
Step-by-step explanation:
Triangles are congruent by SSS (Side-Side-Side) when all three sides of one triangle are equal in length to the corresponding sides of another triangle. According to the SSS postulate, if each side of one triangle is the same length as the corresponding side of another triangle, then the two triangles are congruent. This means they are the same shape and size, even if they are positioned differently in the plane.
To be sure that two triangles are congruent by SSS, you must verify that all three corresponding sides are equal. For example, if triangle ABC has sides of lengths a, b, and c, and triangle DEF has sides of lengths d, e, and f respectively, and if a = d, b = e, and c = f, then triangles ABC and DEF are congruent by the SSS postulate.