ta có :[tex]\Delta KHC\infty \Delta HKA\Rightarrow \frac{HC}{AH}=\frac{HK}{AK}\Rightarrow \frac{HC}{2AH}=\frac{HK}{2AK}=\frac{HC}{AN}=\frac{HM}{AK}[/tex]
mà [tex]\widehat{KHC}=\widehat{KAH} \Rightarrow \Delta AKN\infty \Delta HMC(g.c.g) \Rightarrow \widehat{HMC}=\widehat{KNA}[/tex]