\Rightarrow \frac{1}{2}\times \frac{AH}{HC} = \frac{1}{2}\times \frac{HI}{IC}
\Rightarrow \frac{AH}{BC}=\frac{HD}{IC}
Xét \Delta DHA và \Delta ICB , ta có:
\widehat{AHI}=\widehat{C} (cmt)
\Rightarrow \frac{AH}{BC}=\frac{HD}{IC} (cmt)
\Delta DHA \sim \Delta ICB (c-g-c) (dpcm)