Cm: [tex]\Delta AHE\sim \Delta ACD (g.g)[/tex]
[tex]\Rightarrow \widehat{AHE}=\widehat{ACD}[/tex]
[tex]\widehat{BHM}=\widehat{AHE}[/tex] (đối đỉnh)
[tex]\Rightarrow \widehat{BHM}=\widehat{ACD}[/tex]
Ta có:
[tex]\widehat{BMH}=\widehat{ACD}[/tex] (chắn cung AB)
[tex]\widehat{BHM}=\widehat{ACD}[/tex] (cmt)
[tex]\Rightarrow \widehat{BMH}=\widehat{BHM}[/tex]
[tex]\Rightarrow \Delta BMH[/tex] cân tại [tex]B[/tex]