答(1):∵ ∠AOB =90度 ∠BOC=30度
∴ ∠AOC = ∠AOB - ∠BOC = 60度
∠MON = ∠MOC + ∠CON
= = 1/2 * (∠AOC + ∠COB)= 1/2 * ∠AOB =45度
答(2):如果(1)中,角AOB=角a,其他条件不变,则由(1)知:
∠MON = ∠MOC + ∠CON
= = 1/2 * (∠AOC + ∠COB)= 1/2 * ∠AOB =1/2 * ∠a
答(3):如果(1)中,角AOB=角b,其他条件不变,则同理,由(1)知:
∠MON = ∠MOC + ∠CON
= = 1/2 * (∠AOC + ∠COB)= 1/2 * ∠AOB =1/2 * ∠b
结论:在(1)的条件下,∠MON 总是等于 1/2 * ∠AOB