圓形問題!!!!!pls

2∠DBA=∠DOA(∠ at centre=2∠ at ⊙ce)

2∠BDC=∠BOC(∠ at centre=2∠ at ⊙ce)

x+y=360-∠DOA-∠BOC(∠s at a pt.)
=360-2∠DBA-2∠BDC
=2(180-∠DBA-∠BDC)
=2θ(∠s sum of △)