`#laviken#`
a)Ta có : $\widehat{xOy}$`+`$\widehat{yOz}$`=180^o`
$\Rightarrow$ `2.`$\widehat{yOz}$`+2.`$\widehat{yOz}$`=180^o`
$\Rightarrow$ $\widehat{yOz}$`=180^o/3`
$\Rightarrow$ $\widehat{yOz}$`=60^o`
Lại có :$\widehat{xOy}$`+`$\widehat{yOz}$`=180^o`
$\Rightarrow$ $\widehat{xOy}$`+60^o=180^o`
$\Rightarrow$ $\widehat{xOy}$`=180^o-60^o`
$\Rightarrow$ $\widehat{xOy}$`=120^o`
b) Vì `Om` là tia phân giác của $\widehat{xOy}$
$\Rightarrow$ $\widehat{xOm}$`=$\widehat{yOm}$
Ta có : $\widehat{xOm}$`+`$\widehat{yOm}$`=`$\widehat{xOy}$
$\Rightarrow$ $\widehat{xOm}$`+`$\widehat{yOm}$`=120^o`
$\Rightarrow$ `2.`$\widehat{yOm}$`=120^o`
$\Rightarrow$ $\widehat{yOm}$`=120^o/2=60^o`
Lại có :
Vì `On` là tia phân giác của $\widehat{yOz}$
$\Rightarrow$ $\widehat{yOn}$`=`$\widehat{nOz}$
Ta có : $\widehat{yOn}$`+`$\widehat{nOz}$`=`$\widehat{yOz}$
$\Rightarrow$ $\widehat{yOn}$`+`$\widehat{nOz}$`=60^o`
$\Rightarrow$ `2.`$\widehat{yOn}$`=60^o`
$\Rightarrow$ $\widehat{yOn}$`=60^o/2=30^o`
c) Ta có : $\widehat{mOy}$`+`$\widehat{yOn}$`=`$\widehat{mOn}$
$\Rightarrow$ `60^o``+30^o=`$\widehat{mOn}$
$\Rightarrow$ $\widehat{mOn}$`=90^o`
Vậy $\widehat{mOn}$ là góc vuông tại `O`
