Объяснение:
1 ) ∠BOC + ∠AOB = ∠AOC = 120° ;
∠BOC + 3∠BOC = 120° ;
4∠BOC = 120° ;
∠BOC = 30° ; ∠AOB = 3*30° = 90° . В - дь : ∠BOC = 30° ; ∠AOB = 90° .
2 ) ∠AOB + ∠BOC = ∠AOC = 150° ;
∠AOB + 4∠AOB = 150° ;
5∠AOB = 150° ;
∠AOB = 30° ; ∠BOC = 4*30° = 120°. В - дь : ∠BOC = 120° ; ∠AOB = 30° .
3 ) ∠COD = ∠AOB - ( ∠AOD + ∠COB ) = 125° - ( 20° + 25° ) = 80° .
В - дь : ∠COD = 80° .
4 ) ∠COB = ∠AOB - ( ∠AOD + ∠COD ) = 130° - ( 20° + 45° ) = 65° .
В - дь : ∠COB = 65° .
