Answer:
SSS postulate because three sides of a triangle are are congruent
2. Angle Addition Postulate as they are adding both angles
3. 60 + 40 = m <ABC because it's a substitution
4. 100 = m <ABC as it is simplified already
5. Definition of obtuse angle
AD = DB
Angle ADE = Angle CDB
Angle DAE = Angle DBC (Alternate angles)
Angle DEA = Angle DCB (Alternate angles)
Since you have two congruent angles and one congruent side, triangle ADE is congruent to triangle CDB. This means that DE is congruent to DC implying D is the midpoint of CE.
