Oh my God! This is my problem. I'm quite surprised to see it on IMO. I even doubted that this problem will be on the Shortlist. The story of how I came up with it is quite lengthy, and I don't remember all the details, but I got chain of problems, each time improving former version by doing inversion, watching some new stuff in construction in Geogebra, until finally, in few months came up with the final version of this problem. I actually sent slightly different proposal, and in that statement the fact of this problem was very unexpected for me, so I decided to send it on IMO.Và Shtandenko đã chia sẻ file đề nghị gốc của mình (đề, đáp án, hình vẽ). Cách đặt câu hỏi trong đề gốc có khác một chút so với đề IMO chính thức.
Đề gốc
Lời giải
Theo AoPS. Người đăng: Mr. Math.