You can use the CPCTC (Corresponding Parts of Congruent Triangles are Congruent) property. This means that when two triangles are congruent, all the corresponding parts are congruent to each other.
If two triangles are congruent, then everything in the triangle be congruent. If one triangle has an angle of 50, how can the other triangle not have an angle of 50 and not be conguent. Thus if every part of a triangle is congruent, the every individual part is also congruent
