Answer:
SSS (Side Side Side)
The simplest way to prove that triangles are congruent is to prove that all three sides of the triangle are congruent. When all the sides of two triangles are congruent, the angles of those triangles must also be congruent. This method is called side-side-side, or SSS for short.
SAS (Side-Angle-Side)
A second way to prove the congruence of triangles is to show that two sides and their included angle are congruent. This method is called side-angle-side. It is important to remember that the angle must be the included angle--otherwise you can't be sure of congruence. When two sides of a triangle and the angle between them are the same as the corresponding parts of another triangle there is no way that the triangles aren't congruent. When two sides and their included angle are fixed, all three vertices of the triangle are fixed. Therefore, two sides and their included angle is all it takes to define a triangle; by showing the congruence of these corresponding parts, the congruence of each whole triangle follows.
