$\text{Ta có: $\widehat{B_4}$ = $\widehat{B_2}$ = $45^o$ (đđ)}$
$\text{nên $\widehat{B_2}$ = $\widehat{A_2}$ (= $45^o$)}$
$\text{mà đó là hai góc đồng vị}$
$\text{nên a//b (cái này là mình đặt tên cho 2 đường thẳng nhé)}$
$\text{a/ $\widehat{A_4}$ = $\widehat{B_2}$ = $45^o$ (slt)}$
$\text{b/ $\widehat{B_4}$ = $\widehat{A_4}$ = $45^o$ (đv)}$
$\text{c/ $\widehat{A_4}$ + $\widehat{B_3}$ = $180^o$ (tcp)}$
$\text{T/S: $45^o$ + $\widehat{B_3}$ = $180^o$}$
$\text{⇒ $\widehat{B_3}$ = $180^o$ - $45^o$ = $135^o$}$
$\text{d/ $\widehat{B_1}$ + $\widehat{A_2}$ = $180^o$ (ncp)}$
$\text{$\widehat{A_2}$ = $45^o$}$
$\text{$\widehat{B_1}$ = $\widehat{B_3}$ = $135^o$ (đđ)}$
$\text{HỌC TỐT NHÉ!}$
$Hry_{123}$
