Find smallest C such that 1+(x+y)² <= C·(1+x²)·(1+y²)
Source: German DEMO 2008, grade 11-13, round 4, problem 4
May 22, 2008
functioninequalities
Problem Statement
Find the smallest constant such that for all real
1\plus{}(x\plus{}y)^2 \leq C \cdot (1\plus{}x^2) \cdot (1\plus{}y^2)
holds.