Đáp án:
$\widehat{xOy}+\widehat{xOy'}=180^{\circ}$
$\to \widehat{xOy'}=180-90^{\circ}=90^{\circ}$
$\widehat{xOy'}+\widehat{y'Ox'}=180^{\circ}$
$\to \widehat{y'Ox'}= 180^{\circ}-90^{\circ}=90^{\circ}$
$\widehat{y'Ox'}+\widehat{yOx'}=180^{\circ}$
$\to \widehat{yOx'}=180^{\circ}-90^{\circ}=90^{\circ}$