-△ADG có: AG//HB \(\Rightarrow\dfrac{BD}{AD}=\dfrac{HB}{AG}\Rightarrow\dfrac{AB}{AD}=\dfrac{HB+AG}{AG}\)
-△AEG có: AG//HC \(\Rightarrow\dfrac{CE}{AE}=\dfrac{HC}{AG}\Rightarrow\dfrac{AC}{AE}=\dfrac{HC+AG}{AG}\)
(chắc vậy :v).
\(\dfrac{S_{ADF}}{S_{ABM}}=\dfrac{AD}{AB}.\dfrac{AF}{AM}\); \(\dfrac{S_{ACF}}{S_{ACM}}=\dfrac{AF}{AM}\Rightarrow\dfrac{S_{ACF}}{S_{ABM}}=\dfrac{AF}{AM}\)