ta có$\frac{HD}{GB}=\frac{OD}{GB}$đặt AM=a $\Rightarrow AD=2a;OB=OD=a\sqrt{2}$
$\Rightarrow HD.GB=OB.OD=a\sqrt{2}.a\sqrt{2}=2a^{2}$=AD.BM( vì AM=BM)
$\Rightarrow \frac{HD}{AB}=\frac{BM}{BG}$
$\Rightarrow \widehat{AHB}=\widehat{BMB}$
$\Rightarrow \widehat{HAB}=\widehat{GMB}$
MG song song AH