The complementary angle of the angle AOE is the angle EOB.
(2) because angle DOE= angle DOC, angle COE
Angle DOE=90 degrees
So the angle DOC and the angle COE are complementary.
Because angle COB= angle COE, angle EOB
Angle COB=90 degrees
So the angle COE and the angle EOB are complementary.
So angle DOC= angle EOB