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max C: (x + y +z + u)^2 >= Cyz (V Soros Olympiad 1998-99 Round 1 11.2)

Source:

May 25, 2024
algebrainequalities

Problem Statement

Find the greatest value of CC for which, for any x,y,z,ux, y, z,u, and such that for 0xyzu0\le x\le y \le z\le u, holds the inequality (x+y+z+u)2Cyz.(x + y +z + u)^2 \ge Cyz .