[tex]\it a)\ \ \mathcal{A}_{ABC}=\dfrac{\ell^2\sqrt3}{4}=\dfrac{12^2\sqrt3}{4}=\dfrac{12\cdot12\sqrt3}{4}=3\cdot12\sqrt3=36\sqrt3\ cm^2[/tex]
b) AD - înălțime în Δ ABC ⇒ AD - mediană ⇒ DC = 12:2=6cm
[tex]\it \mathcal{P}_{DCFE} =2(DC+CF)=2(6+12)=2\cdot18=36\ cm[/tex]
[tex]c)\ \it AE\perp BC,\ \ FC\perp BC \Rightarrow ACFE-\ trapez\\ \\ \mathcal{A}_{ACFE}=\mathcal{A}_{ACD}+\mathcal{A}_{DCFE}=\dfrac{\mathcal{A}_{ABC}}{2}+DC\cdot CF =\\ \\ \\ =\dfrac{\it36\sqrt3}{\it2}+6\cdot12 =18\sqrt3+72=18(\sqrt3+4)\ cm^2[/tex]
