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MathNet 2017-part-02 — 176 problems (EN–VI) Question 128

Math Olympiad Vault · MathNet 2017-part-02 — 176 problems (EN–VI)

Question 128

Let $ABC$ be a triangle whose three angles are acute and let $\Gamma$ be its circumcircle. The tangent to $\Gamma$ at $A$ meets $(BC)$ at $P$. Let $M$ be the midpoint of $[AP]$. The line $(BM)$ meets $\Gamma$ again at $R$ and the line $(PR)$ meets $\Gamma$ again at $S$.

Show that $(AP)$ and $(CS)$ are parallel.

Question illustration