solution;
They are congruent triangles their sides will be congruent.
Since ABCD is a parallelogram, opposite sides are parallel by definition.
AD is parallel to BC.
Sides AB and DC are parallel.
Triangles DCA and BAC are congruent by ASA.
AD is congruent to BC by CPCTC.
DC is congruent to BA by CPCTC.
The CPCTC theorem just says that if two triangles are congruent, their corresponding parts are congruent.
