Dễ dàng CM được $\triangle{EMN} \sim \triangle{EFD} \implies \angle{NME} = \angle{DFE}$, mà $\angle{DFE} = 90^\circ - \angle{FDE} = 90^\circ - \angle{DEG}$
$\implies \angle{NME} + \angle{DEG} = 90^\circ$
$\iff EG \perp MN$
Tiếp tục CM $\triangle{MIE} \sim \triangle{MEN} \implies \dfrac{S_{MIE}}{S_{MEN}} = \left(\dfrac{ME}{MN}\right)^2$
$\iff S_{MIE} = \left(\dfrac{ME}{MN}\right)^2\cdot S_{MEN}$
Lại có $\triangle{MEN} \sim \triangle{FED} \implies \dfrac{S_{MEN}}{S_{FED}} = \left(\dfrac{MN}{FD}\right)^2$
$\iff S_{MEN} = \left(\dfrac{MN}{FD}\right)^2\cdot S_{FED}$
$\implies S_{MIE} = \left(\dfrac{ME}{FD}\right)^2\cdot S_{FED}$
Tự tính các cạnh rồi thay vào