$\widehat{DMC}=\widehat{DBM}+\widehat{BDM} =\widehat{DME}+\widehat{EMC}$mà$\widehat{DBM}=\widehat{DME}$
$\Rightarrow \widehat{BDM}=\widehat{EMC}$
xét$\Delta BDM và \Delta CME$ có
$\widehat{B}=\widehat{C}$
$\widehat{BDM}=\widehat{EMC}$ ( cmt)
$\Rightarrow \Delta BDM$~$\Delta CME$ ( g.g)
b,Theo a, $\Rightarrow \frac{BD}{BM}=\frac{CM}{CE}$
$\Leftrightarrow BD.CE=BM.CM= conts$( đpcm)
c, theo a $\frac{BD}{CM}=\frac{DM}{ME}$
$\Leftrightarrow\frac{BD}{BM}=\frac{DM}{ME}$
Lại có $\widehat{DME}= \widehat{DBM}$
$\Rightarrow \Delta DBM$~$\Delta DME$
$\Rightarrow \widehat{BDM}=\widehat{MDE}$(đpcm)
=.= z nha