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MathNet 2015-part-03 — 191 problems (EN–VI) Question 82

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

Question 82

Let $ABC$ be a triangle inscribed into a circle $\Omega$ with center $O$. A circle $\Gamma$ with center $A$ meets the side $BC$ at points $D$ and $E$ such that $D$ lies between $B$ and $E$. Moreover, let $F$ and $G$ be the common points of $\Gamma$ and $\Omega$. We assume that $F$ lies on the arc $AB$ of $\Omega$ not containing $C$, and $G$ lies on the arc $AC$ of $\Omega$ not containing $B$. The circumcircles of the triangles $BDF$ and $CEG$ meet the sides $AB$ and $AC$ again at $K$ and $L$, respectively. Suppose that the lines $FK$ and $GL$ are distinct and intersect at $X$. Prove that the points $A$, $X$, and $O$ are collinear.

Question illustration
Figure 1