Which of the following equal(s) ∠AOB?
∠AOD+∠DOC+∠COB
∠AOC+∠COB
∠AOD+∠DOB
Note that ∠AOB can be obtained in the following different ways:
∠AOD+∠DOB,
∠AOC+∠COB and
∠AOD+∠DOC+∠COB.
Also note that ∠AOD+∠COB does not equal ∠AOB. In fact, ∠AOD+∠COB = ∠AOB−∠DOC since
∠AOD+∠DOC+∠COB=∠AOB.