IMO 2011 problem 6 Geometry

This link may be useful.There are quite a few solutions there.

http://www.artofproblemsolving.com/Forum/viewtopic.php?p=2365045&sid=0cdd97cc9547c2079a4ba23c56ba8f74#p2365045

In fact,this was the toughest problem at the IMO 2011.It was G8 on the Shortlist,meaning a hard problem. The IMO committee actually ended up misjudging the difficulty of the problems,as evident from the way they were numbered on the Shortlist.

Solution of problem 6 IMO 2011: I use the method of analytic geometry. Starting with the unit circle and 3 arbitrary points A,B C on its circumference, I found after laborious computations the equation of the second circumscribed circle. It is possible to construct the equation which is the tangent-condition of the 2 circles. Substitution completes the proof. In the case of a isosceles triangle the centre M of the second circle describes a limacon of Pascal, which degenerates in a circle in the case of a equilateral triangle Then that circle coincides the original unit circle

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