Question

How can they been proven congruent ?

Answer 1

The two angles marked are congruent.
That is one pair of congruent angles.   ------->    A
Then the vertical angles are congruent.
That is a second pair of congruent angles.    -------> A
Finally, we have the two sides marked congruent.
That is one pair of congruent sides.    ------> S

Put together what we have above, and it gives us AAS.