sửa đề : \(Cm:AE^2=EK\cdot EM\)
+ BK // AD \(\Rightarrow\frac{EK}{AE}=\frac{BK}{AD}=\frac{BK}{BC}\)
+ AB // DM \(\Rightarrow\frac{AE}{ME}=\frac{AB}{DM}\)
+ AB // CM \(\Rightarrow\frac{BK}{CK}=\frac{AB}{CM}\Rightarrow\frac{BK}{BK+CK}=\frac{AB}{AB+CM}\)
\(\Rightarrow\frac{BK}{BC}=\frac{AB}{DM}\Rightarrow\frac{EK}{AE}=\frac{AE}{ME}\)
\(\Rightarrow AE^2=EK\cdot EM\)