The complementary angle of (1) angle COE is angle COD.

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