Congruent Triangles - Two angles and included side (ASA) Definition: Triangles are congruent if any two angles and their included side are equal in both triangles. There are five ways to test that two triangles are congruent. This is one of them (ASA). For a list see Congruent Triangles. If any two angles and the included side are the same in both triangles, then the triangles are congruent.
Congruent triangles can be rotated and/or mirror images of each other (reflected). (See Congruent triangles.) In the figure on the right, the two triangles have all three corresponding sides equal in length and so are still congruent, even though one is the mirror image of the other and rotated.