`Xét` `ΔOED` `và` `ΔOKB:`

`hat{ODE} = hat{OBK}.` (sltr)

`hat{OED} = hat{OKB}.` (sltr)

`⇒ ΔOED ~ ΔOKB. (g-g)`

`⇒ hat{EOD} = hat{KOB}`

`Lại` `có:`

`hat{KOB} + hat{KOD} = hat{DOB} = 180^{o}.`

`⇒ hat{EOD} + hat{KOD} = hat{KOE} = 180^{o}.`

$\textit{⇒ E, O, K thẳng hàng.}$

$\textit{andychuongpham}$