Two angles are supplementary when they add up to 180 degrees.
1. Consider angle ∠COB:
m∠DOC+m∠COB=m∠DOB=180°.
This means that angles ∠DOC and ∠COB are supplementary.
2. Consider angle DOA:
m∠DOC+m∠DOA=m∠COA=180°.
This means that angles ∠DOC and ∠DOA are supplementary.
Answer: 1. ∠COB; 2. ∠DOA
