Giải thích các bước giải:
a) Ta có:
$\left\{ \begin{array}{l}
\widehat Cchung\\
\widehat {AKC} = \widehat {BHC} = {90^0}
\end{array} \right. \Rightarrow \Delta AKC \sim \Delta BHC\left( {g.g} \right)$
b) Ta có:
$\begin{array}{l}
\Delta AKC \sim \Delta BHC\\
\Rightarrow \dfrac{{AC}}{{BC}} = \dfrac{{KC}}{{HC}}\\
\Rightarrow \dfrac{{AH + HC}}{{BC}} = \dfrac{{\dfrac{{BC}}{2}}}{{HC}}\\
\Rightarrow B{C^2} = 2\left( {AH + HC} \right)HC = 2\left( {7 + 2} \right).2 = 36\\
\Rightarrow BC = 6
\end{array}$
Vậy $BC=6$