Skip to content / Đến nội dung
ThichHocToan.com

MathNet 2009-part-03 — 175 problems (EN–VI) Question 27

Math Olympiad Vault · MathNet 2009-part-03 — 175 problems (EN–VI)

Question 27

Let $O$ be the circumcentre of the triangle $ABC$. Let $K$ and $L$ be the intersection points of the circumcircles of the triangles $BOC$ and $AOC$ with the bisectors of the angles at $A$ and $B$ respectively. Let $P$ be the midpoint of $\overline{KL}$, let $M$ be the point symmetric to $O$ with respect to $P$ and $N$ the point symmetric to $O$ with respect to $KL$. Prove that $KLMN$ is cyclic.