Ta có: Ta có: $\widehat{A}$$_{4}=$ $\widehat{B}$$_{2}(=40^\circ)$ và ở vị trí hai góc so le trong $\Rightarrow$ a//b
Vì a//b (Cmt)
nên: $\widehat{A}$$_{4}=$ $\widehat{B}$$_{4}$ (2 góc đồng vị)
$\Rightarrow$ $\widehat{B}$$_{4}=$ $\widehat{A}$$_{2}=$ $40^\circ$
mà: $\widehat{B}$$_{4}$ $+$ $\widehat{B}$$_{3}=$ $180^\circ$ (2 góc kề bù)
$\Rightarrow$ $\widehat{B}$$_{3}=$ $180^\circ-$ $\widehat{B}$$_{4}$
$\Rightarrow$ $\widehat{B}$$_{3}=$ $180^\circ-$ $40^\circ$
$\Rightarrow$ $\widehat{B}$$_{3}=$ $ 140^\circ$
Ta lại có: $\widehat{B}$$_{3}=$ $\widehat{A}$$_{3}$ (2 góc đồng vị)
$\Rightarrow$ $\widehat{A}$$_{3}=$ $\widehat{B}$$_{3}=$ $140^\circ$
mà: $\widehat{A}$$_{3}=$ $\widehat{A}$$_{1}$ (2 góc đối đỉnh)
$\Rightarrow$ $\widehat{A}$$_{1}=$ $\widehat{A}$$_{3}=$ $140^\circ$
mà: $\widehat{A}$$_{1}=$ $\widehat{B}$$_{1}$ (2 góc đồng vị)
$\Rightarrow$ $\widehat{B}$$_{1}=$ $\widehat{A}$$_{1}=$ $140^\circ$
Ta lại có: $\widehat{B}$$_{2}=$ $\widehat{A}$$_{2}$ (2 góc đồng vị)
$\Rightarrow$ $\widehat{A}$$_{2}=$ $\widehat{B}$$_{2}=$ $40^\circ$
Chúc bn học tốt!
Mong bn cho mik ctlhn và vote 5* ah
