what  is congruence .

In geometry, two figures or objects are congruent if they have the same shape and size, or if one has the same shape and size as the mirror image of the other. More formally two sets of points are called congruent. 

Congruence Of Triangles :- Two triangles are congruent  if their corresponding sides are equal in length and corresponding angles are equal in size.

If  triangle ABC is congruent to triangle DEF, the relationship can be written mathematically as:

ΔABC ΔDEF

Hope this helps you.