Skip to content / Đến nội dung
ThichHocToan.com

MathNet 2015-part-03 — 191 problems (EN–VI) Question 181

Math Olympiad Vault · MathNet 2015-part-03 — 191 problems (EN–VI)

Question 181

Let $ABC$ be an acute triangle with $AB \gt AC$. Prove that there exists a point $D$ with the following property: whenever two distinct points $X$ and $Y$ lie in the interior of $ABC$ such that the points $B$, $C$, $X$, and $Y$ lie on a circle and
$$
\angle AXB - \angle ACB = \angle CYA - \angle CBA
$$
holds, the line $XY$ passes through $D$.