Question

Answer 1

 Vẽ tia Bz // Ax // Cy

Do Bz // Ax

⇒ ∠zBA = ∠xAB = 60⁰ (so le trong)

Do Bz // Cy

⇒ ∠zBC = ∠yCB = 20⁰ (so le trong)

⇒ ∠ABC = ∠zBA + ∠zBC

= 60⁰ + 20⁰

= 80⁰

Answer 2

Kẻ thêm Bz//Cy//Ax  

Ta có: Ax//Bz 

\(\Rightarrow\widehat{xAB}=\widehat{zBA}\) (so le trong)

\(\Rightarrow\widehat{\text{z}BA}=60^o\)

Ta có: Bz//Cy 

\(\Rightarrow\widehat{\text{y}CB}=\widehat{zBC}\)

\(\Rightarrow\widehat{zBC}=20^o\)

Mà: \(\widehat{zBA}+\widehat{zBC}=\widehat{ABC}\) (kề)

\(\Rightarrow\widehat{\text{A}BC}=60^o+20^o=80^o\)