... CHU,O,NG 45Ð`Ê THI OLYMPIC TO´AN BA LAN45.1. Ðê`b`aiB`ai 45.1. Cho D l`a m.ôt¯diê,m trên c.anh ... n´o l`a(7, −1), (7, 13), (9, −1), (9, 13), (3, 1), (3, 11)(13, 1), (13, 11), (1, 5), (1, 7), (15, 5), (15, 7).Do¯d´o m˜ôi c.˘ap (xi, xi+1) (v´o,i xn+1= x1) ph,ai ... j≤nf{ai,aj}(x) + f{bi,bj}(x) ≤1≤i< j≤nf{ai,aj}(x). 22 Chu,o,ng 42. Ðê` thi olympic to´an ItalyV`ı ch´ung ta xây 2 câ`u d˜ân¯dê´n m˜ôi nh`a v`a bâ´t...