Δευτέρα, 7 Νοεμβρίου 2016

China National Mathematical Olympiad 2016 - Problem 2

In $\triangle AEF$, let $B$ and $D$ be on segments $AE$ and $AF$ respectively, and let $ED$ and $FB$ intersect at $C$. 
Define $K,L,M,N$ on segments $AB,BC,CD,DA$ such that 
                                   $\dfrac{AK}{KB}=\dfrac{AD}{BC}$ 
and its cyclic equivalents. Let the incircle of $\triangle AEF$ touch $AE,AF$ at $S,T$ respectively; let the incircle of $\triangle CEF$ touch $CE,CF$ at $U,V$ respectively. 
Prove that $K,L,M,N$ concyclic implies $S,T,U,V$ concyclic.

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