Giải thích các bước giải:
Gọi $PN\cap MQ=I'$
$\rightarrow \dfrac{I'N}{I'P}=\dfrac{I'Q}{I'M}=\dfrac{QN}{PM}=\dfrac{RQ}{RP}$
$\rightarrow RI'// MP//QN\rightarrow I'=PN\cap RH\rightarrow I\equiv I'$
$\rightarrow \dfrac{IR}{QN}=\dfrac{PI}{PN}=\dfrac{MI}{MQ}=\dfrac{IH}{QN}$
$\rightarrow IR=IH$
