B1. 1) ∠AOB = 5∠AOC, ∠AOC, ∠BOC - ?

1. ∠AOB = 5∠AOC. Пусть ∠AOC = x, тогда ∠AOB = 5x.
2. ∠AOB = ∠AOC + ∠BOC. 5x = x + ∠BOC. ∠BOC = 4x.
3. Если ∠AOB = 150°, то 5x = 150°, x = 30°. ∠AOC = 30°, ∠BOC = 4 * 30° = 120°.