Đáp án:
Giải thích các bước giải:
$\text{a,Ta có:}$
$\widehat{BAx}+\widehat{ABy}=40°+140°=180°$
$=>Ax\parallel By$
$\text{Mà $By\parallel Cz$}$
$=>Ax\parallel Cz$
$b,Ax\parallel By$
$=>Ax║By'$
$\text{$\widehat{ABy'}=\widehat{BAx}=40°$(2 góc so le trong)}$ (1)
$By\parallel Cz$
$=>By'║Cz$
$=>\widehat{BCz}+\widehat{y'BC}=180°$
$=>130°+\widehat{y'BC}=180°$
$=>\widehat{y'BC}=50°$ (2)
$\text{Từ $(1);(2)=>\widehat{ABy'}+\widehat{y'BC}=40°+50°=90°=\widehat{ABC}$}$
$=>AB\bot BC$
