2o 15 Is there any other way to find the angle mon of the mathematics problem in Hainan senior high school entrance examination?
(1), the angle MOC=30 degrees, the angle NOC= 15 degrees, and the angle MON=45 degrees. (2) given the angle AOB=a and other conditions unchanged, the angle AOC=a-30 degrees, then the angles AOC(3) and (4) of the angle MOC= 1/2 can be in the above manner.