@Moonnek2008
#Hoidap247
$\text{a. Ta có trong ΔABC vuông tại A có:}$
$\text{-$\widehat{BAC}$=90°}$
$\text{→$\widehat{ABC}$+$\widehat{ACB}$=90° (phụ nhau)}$
$\text{Vậy $\widehat{ABC}$+$\widehat{ACB}$=90°}$
$\text{b. So sánh:}$
$\text{Ta có: $\widehat{HAx}$= $\widehat{BHA}$ và $\widehat{HAy}$= $\widehat{CHA}$(so le trong)}$
$\text{mà $\widehat{BAC}$=90°→$\widehat{BAx}$=$\widehat{CAy}$=$\frac{90°}{2}$=45°}$
$\text{→$\widehat{ACB}$=$\widehat{CAy}$=45°}$
$\text{$\widehat{BAC}$=90°→$\widehat{CAH}$=$\widehat{BAH}$=$\frac{90°}{2}$=45°}$
$\text{→$\widehat{BAH}$=$\widehat{C}$}$
