Part 1: So, we have two triangles to compare. We can use the Triangle Sum theorem, which says the angles in a triangle add up to 180 degrees. For one triangle, angles <X, <Y, and <Z add up to 180, and we know two angles (<X and <Z), so we can find <Y. For the other triangle, we already know angle <D, <B, and the third angle will be similar since the rest will add up to 180 as well.
Then, we can use the AAS (Angle-Angle-Side) congruency theorem because we have two angles and one side (XY = CD) for both triangles. This means the triangles are congruent.
Part 2: Triangle XYZ = Triangle DBC (or XYZ = DBC)