∠ACB = ∠ABC = α => ∠BDC = α => ∠DBC = α -21°
∠BDC + ∠DCB + ∠DBC = 180° => 3α - 21 = 180 => α = 67° => x = 180 - 2α = 180 - 134 = 46°
ответ: 46°
