\(ME//KA→\dfrac{CE}{CM}=\dfrac{EA}{KM}\) (ĐL Talet)
\(KA//DM→\dfrac{BD}{BM}=\dfrac{AD}{KM}\) (ĐL Talet)
Ta có: \(\begin{cases}\widehat{D}=\widehat{BAK}\\\widehat{AED}=\widehat{KAE}\\\widehat{BAK}=\widehat{KAE}\end{cases}\\→\widehat{D}=\widehat{AED}\)
\(→ΔAED\) cân tại \(A\)
\(→EA=AD\\→\dfrac{EA}{KM}=\dfrac{AD}{KM}\\→\dfrac{CE}{CM}=\dfrac{BD}{BM}\)
mà \(CM=BM\)
\(→BD=CE\)
