Đáp án+Giải thích các bước giải:
$\text{Bài1:}$
$\text{Xét ΔABC có:}$
$\text{$\widehat{A}$+$\widehat{B}$+$\widehat{C}$ = $180^o$ ⇔ $\widehat{C}$ = $180^o$ - $57^o$-$63^o$ = $60^o$}$
$\text{Bài2:}$
$\text{Ta có: $\widehat{A}$ + $\widehat{B}$ + $\widehat{C}$ = $180^o$ ⇔ $\widehat{B}$ = $180^o$ - $45^o$ - $75^o$ = $60^o$}$
$\text{⇒ $\widehat{ABE}$ = $\widehat{B}$:2 = $60^o$ :2 = $30^o$}$
$\text{Bài3:}$
$\text{Xét ΔABC vuông tại A có: }$
$\text{$\widehat{B}$ + $\widehat{C}$ = $90^o$ ⇔ $\widehat{C}$ = $35^o$}$
