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MathNet 2026 — Part 11 Question 8

Math Olympiad Vault · MathNet 2026 — Part 11

Question 8

In a scalene triangle $A B C$, $I$ is the incenter and $C N$ is the bisector of angle $C$. The line $C N$ meets the circumcircle of $A B C$ again at $M$. The line $\ell$ is parallel to $A B$ and touches the incircle of $A B C$. The point $R$ on $\ell$ is such that $C I \perp I R$. The circumcircle of $M N R$ meets the line $I R$ again at $S$. Prove that $A S = B S$.