If ∠ BDC = α + 2 / 3 ∠ a, α is obtained

If ∠ BDC = α + 2 / 3 ∠ a, α is obtained

The results show that: DBC = 2 ∠ abd, DCB = 2 ∠ ACD, BDC = α + 2 / 3 ∠ a, a = 180 - ∠ ABC - ∠ ACB = 180-1.5 ∠ dbc-1.5 ∠ DCB ∠ BDC = 180 - ∠ DBC - ∠ DCB, and BDC = α + 2 / 3 ∠ a = α + 2 / 3 (180-1.5 ∠ dbc-1.5 ∠ DCB) = α + 120 - ∠ DBC - ∠ DCB, so α = 60