Ke DN ta co : DN//EB//EQ \RightarrowQC=QN
GOI O LA GIAO DIEM CUA CAC DUONG TRUNG TUYEN
DAT CQ=a QO=b ON=c
TA CO HE PHUONG TRINH SAU: a=b+c
( a+b)/(a+b+c)=2/3
TU DO \Rightarrowa=3c/2 VA b=c/2
\Rightarrowa/b=3\Rightarrowb/(a+b)=1/4
TUONG TU \RightarrowOP/OA=1/4
\RightarrowTG OQP ~TG OCA\RightarrowQP//AC
\RightarrowPQ=AC/4
TU DO \Rightarrow\RightarrowVA\Rightarrow DPCM