$\widehat{AOC} + \widehat{BOC} = 180^{\circ}$ ( hai góc kề bù )
Vì $\widehat{AOC} - \widehat{BOC} = 50^{\circ}$
$→ \widehat{AOC} = \widehat{BOC} +50^{\circ}$
$→ 2\widehat{BOC} + 50^{\circ} = 180^{\circ}$
$→ 2\widehat{BOC} = 130^{\circ}$
$→ \widehat{BOC} = 65^{\circ}$
$→ \widehat{AOC} = 115^{\circ}$
$→ \widehat{BOD} = \widehat{AOC} = 115^{\circ}$
$→ \widehat{AOD} = \widehat{BOC} = 65^{\circ}$