Mhm.... Word problems.. So! Angle Side Angle :) proving that 2 triangles are equal. You need to prove that DC is equal to BA. Now.... DB == AC. which you can subtract BC from both sides! DB-BC = AC-CB. leaving you with DC= AB
Now by Side Angle Side, The angles are =, 2 sides are equal, means the 2 triangles are equal :) If the triangles are equal, the 2 remaining sides must be equal
