Giải thích các bước giải:
Ta có :
$MD\perp BC\to \widehat{DMC}=\widehat{ABC}(+\widehat{ACB}=90^o)$
$\to \Delta ABC\sim\Delta CMD(g.g)$
$\to\dfrac{AC}{CD}=\dfrac{AB}{CM}$
$\to \dfrac{AC}{CD}=\dfrac{AB}{AM}$
$\to\Delta ABM\sim\Delta CAD(c.g.c)\to\widehat{DAC}=\widehat{ABM}\to AD\perp BM$