Explanation:
The triangles can be shown congruent by showing either of an angle or side is congruent in addition to the side marked in the diagram. We choose to show angles A and B are congruent by showing ΔCAD ≅ ΔCBD.
Statement . . . . Reason
CD⊥AB, AD≅BD, DE⊥CA, DF⊥CB . . . . given
CD≅CD . . . . reflexive property of congruence
ΔCDA ≅ ΔCDB . . . . LL congruence postulate
∠A≅∠B . . . . CPCTC
ΔADE ≅ ΔBDF . . . . HA congruence postulate
