Giải thích các bước giải:
Gọi $AH\cap CK=D\rightarrow \widehat{\vec{AH},\vec{CK}}=\widehat{ADC}=\widehat{DHC}+\widehat{DCH}$
Mà $AH\perp BC\rightarrow\widehat{DHC}=90^o$
Lại có $AB\perp AC\rightarrow \widehat{C}+\widehat{B}=90^o\rightarrow\widehat{ACB}=40^o$
$\rightarrow\widehat{DCH}=\dfrac{1}2\widehat{ACH}=20^o$
$\rightarrow\widehat{ADC}=90^o+20^o=110^o$
$\widehat{\vec{AH},\vec{CK}}=110^o$