A triangle is a polygon formed by three-line segments joining and forming three internal angles. Two triangles can be said to be congruent if their corresponding sides are equal in their length and their corresponding angles are equal in their measure. For example, if there are two triangle, Δ ABC and Δ DEF, where AC = DF, BC = EF, AB = DE, and ∠A =∠D, ∠B = ∠E, ∠C = ∠F, we can say Δ ABC is congruent to, ΔDEF.
A triangle can be identified by its six measures, which are three angles and three sides. Two triangles are congruent if all these six measures are equal. But while trying to determine congruence, if we have three particular specific measures it will be enough.
If we can establish that two given triangles are congruent, then we can say that all corresponding sides and angles of the two triangles are the same. Hence if we prove that two triangles are congruent using any one of the congruency theorems, we can find the measurement of angles or sides of one triangle if we know the corresponding measurements in the other triangle which is congruent to it.