Đáp án:
$\widehat{O_4}+\widehat{O_2}+\widehat{O_1}+\widehat{O_3}=360°$( Tổng hai góc bẹt )
$⇒\widehat{O_3}=360°-\widehat{O_4}+\widehat{O_2}+\widehat{O_1}=360°-300°=60°$
Ta có :
$\widehat{O_3}=\widehat{O_1}=60°$(2 góc đối đỉnh)
$\widehat{O_2}+\widehat{O_1}=180°$( 2 góc kề bù )
$⇒\widehat{O_2}=180°-\widehat{O_1}=180°-60°=120°$
$\widehat{O_4}=\widehat{O_2}=120°$( 2 góc đối đỉnh )
Vậy $\widehat{O_4}=\widehat{O_2}=120°;\widehat{O_3}=\widehat{O_1}=60°$