\(1,\widehat{KDA}+\widehat{KAD}=90^0\left(\Delta AKD.vuông.tại.K\right)\\ \widehat{KAD}+\widehat{KAB}=\widehat{BAC}=90^0\\ \Rightarrow\widehat{KDA}=\widehat{KAB}\\ \left\{{}\begin{matrix}\widehat{KDA}=\widehat{KAB}\\\widehat{AKD}=\widehat{AHB}\left(=90^0\right)\\AD=AB\left(gt\right)\end{matrix}\right.\Rightarrow\Delta HAB=\Delta KDA\left(ch-gn\right)\\ 2,DE//KH\Rightarrow\widehat{EDH}=\widehat{KHD}\left(so.le.trong\right)\\ \left\{{}\begin{matrix}\widehat{EDH}=\widehat{KHD}\\\widehat{DKH}=\widehat{DHE}\left(=90^0\right)\\DH.chung\end{matrix}\right.\Rightarrow\Delta KDH=\Delta EDH\left(ch-gn\right)\)
\(\Rightarrow\widehat{KDH}=\widehat{EHD}\\ 3,\left\{{}\begin{matrix}HA=DK\left(\Delta HAB=\Delta KDA\right)\\DK=EH\left(\Delta KDH=\Delta EDH\right)\end{matrix}\right.\Rightarrow AH=EH\left(=DK\right)\)
