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MathNet 2020 — Math Olympiad Vault — Part 03 Question 78

Math Olympiad Vault · MathNet 2020 — Math Olympiad Vault — Part 03

Question 78

Let $\triangle ABC$ be a triangle inscribed in a unit circle with center $O$. Let $I$ be the incenter of $\triangle ABC$, and let $D$ be the intersection of $BC$ and the angle bisector of $\angle BAC$. Suppose that the circumcircle of $\triangle ADO$ intersects $BC$ again at a point $E$ such that $E$ lies on $IO$. If $\cos A=\frac{12}{13}$, find the area of $\triangle ABC$.