ITOT 44 Spring 2023 · THPT · O (Basic) Question 3

Let $I$ be the incenter of triangle $ABC$, and let $N=BI\cap AC$. The tangent at $A$ to the circumcircle of $AIN$ meets the tangent at $C$ to the circumcircle of $CIN$ at $D$. Prove that $AC\perp DI$.