Bài 1:
$\widehat{BOD} = \frac{1}{2}× 60° = 30° $
Ta có :
$\widehat{AOC}$ + $\widehat{COD}$ + $\widehat{DOB}$ = $\widehat{AOB}$
$60° + \widehat{COD} + 30° = 180° $
$⇒ \widehat{COD} = 90° $
$⇒ OC ⊥ OD $
Bài 2 :
Ta có :
$\widehat{AOE} = \widehat{BOF}$ và $\widehat{COE} = \widehat{COF}$
$⇒ \widehat{AOC} = \widehat{COB}$
$⇒ \widehat{AOC} = \widehat{COB} = 180° : 2 $
$⇒ \widehat{COB} = 90° $
$⇒ OC ⊥ AB $