Giải thích các bước giải:
$\dfrac{S_{AEF}}{S_{ABF}}=\dfrac{AE}{AB}$
$\dfrac{S_{ABF}}{S_{ABC}}=\dfrac{AF}{AC}$
$\rightarrow \dfrac{S_{AEF}}{S_{ABF}}.\dfrac{S_{ABF}}{S_{ABC}}=\dfrac{AE}{AB}.\dfrac{AF}{AC}$
$\rightarrow \dfrac{S_{AEF}}{S_{ABC}}=\dfrac{AE.AF}{AB.AC}$