Given two triangles, ADB and CBD
So,
1. the measure of < D = the measure of angle < B
2. CB = AD
3. BD = DB
so, the triangle ADB is congruent to the triangle CBD by SAS [ side - angle - side ]
So, the corresponding parts are congruent :
So,
1. the measure of angle A = the measure of angle C
2. the measure of angle B = the measure of angle D
3. AB = CD