olymmath

KMO 1998

Korean Mathematical Olympiad 1998.

Other problems

Problem 2

Let DD , EE , FF be points on the sides BCBC , CACA , ABAB respectively of a triangle ABCABC . Lines ADAD , BEBE , CFCF intersect the circumcircle of ABCABC again at PP , QQ , RR , respectively.Show that: ADPD+BEQE+CFRF≥9\frac{AD}{PD}+\frac{BE}{QE}+\frac{CF}{RF}\geq 9 and find the cases of equality.

Problem 5

Let II be the incenter of triangle ABCABC , O1O_1 a circle through BB tangent to CICI , and O2O_2 a circle through CC tangent to BIBI . Prove that O1O_1 , O2O_2 and the circumcircle of ABCABC have a common point.