Number of angles less than 180° in Fig. 2.17 is ______ and their names are __________.
12
∠OAB, ∠OBA, ∠AOB, ∠AOC, ∠OAC, ∠OCA, ∠OCD, ∠COD, ∠ODC, ∠BAC, ∠DCA, ∠DOB.
24
Number of angles less than 180° in Fig. 2.17 is ______ and their names are __________.
12
∠OAB, ∠OBA, ∠AOB, ∠AOC, ∠OAC, ∠OCA, ∠OCD, ∠COD, ∠ODC, ∠BAC, ∠DCA, ∠DOB.