a,\(AB\perp AC\) => \(OD\perp AC\)
=> \(\widehat{ODC}=90^o\)
Xét \(\Delta ABC\) và \(\Delta DOC\) có :
\(\widehat{C}:chung\)
\(\widehat{BAC}=\widehat{ODC}=90^o\)
=> \(\Delta ABC\sim\Delta DOC\left(g.g\right)\)
b, Xét \(\Delta AOH\) và \(\Delta DOA\) có :
\(\widehat{O}:chung\)
\(\widehat{OAH}=\widehat{ODA}=90^o\)
=> \(\Delta AOH\sim\Delta DOA\left(g.g\right)\)