Step-by-step explanation:
1. You already got the first step, where D is the midpoint of AC and AB is congruent to BC, since it's given.
2. AD will be congruent to DC, via the definition of a midpoint (a midpoint is the middle point of a line segment, and it splits the segment into two congruent parts)
3. BD is equal to BD, via reflexive property. ( It's a shared side between the two triangles)
4. that means that ΔADB ≅ΔCDB via SSS rule.
5. ∠ABD ≅∠CDB by CPCTC (corresponding parts of congruent triangles are congruent)
Hope this helps! :)
