`Ta` `có:`
$\widehat{P1}$+$\widehat{P2}$ =`180^o` (kề bù)
`->` $\widehat{P2}$ = `180^o` `-` `120^o` = `60^o`
$\begin{cases} \widehat{P1}=\widehat{P3}=120^o(đối đỉnh)\\\widehat{P2}=\widehat{P4}=60^o\\ \end{cases}$
`Ta` `lại` `có:`
$\widehat{Q3}$`+`$\widehat{Q2}$=`180^o` (kề bù)
`->` $\widehat{Q2}$ = `180^o` `-` `80^o` = `100^o`
$\begin{cases} \widehat{Q3} = \widehat{Q1}=80^o(đối đỉnh)\\\widehat{Q2}=\widehat{Q4}=100^o\\ \end{cases}$
`Vậy` $\widehat{P2}$ =`60^o` ; $\widehat{P3}$ =`120^o` ; $\widehat{P4}$ = `60^o`
`Và` $\widehat{Q2}$ =`100^o` ; $\widehat{Q1}$ =`80^o` ; $\widehat{Q4}$ = `100^o`
