[tex]\it Ducem\ BF\perp AC\ . \ \ Rezult\breve a\ c\breve a\ d(B,\ AC)=BF\ .\\ \\ \\ \mathcal{A}_{ABC}=\dfrac{BC\cdot AD}{2}=\dfrac{18\cdot \not6\ ^3}{\not2\ _1}=54\ cm^2\\ \\ \\ \mathcal{A}_{ABC}=\dfrac{AC\cdot BF}{2} \Rightarrow 54=\dfrac{12\cdot BF}{2} \Rightarrow 54=6\cdot BF\bigg|_{:6} \Rightarrow BF=9\ cm\\ \\ \\ R\breve aspunsul\ corect\ este\ c)\ 9\ cm[/tex]
