Skip to content / Đến nội dung
ThichHocToan.com

MathNet 2015-part-02 — 191 problems (EN–VI) Question 160

Math Olympiad Vault · MathNet 2015-part-02 — 191 problems (EN–VI)

Question 160

Let $ABC$ be a triangle that is not isosceles at $A$, and $\Gamma$ its circumcircle. Let $N$ be the midpoint of the arc of $\Gamma$ between $B$ and $C$ that contains $A$. Let $I$ be the incentre of $ABC$, $J$ the centre of the $A$-excircle of $ABC$, and $K$ the intersection point of $BC$ with the external bisector of $\angle BAC$.

Show that $(JN) \perp (IK)$.