A Minimum With a Surprising Constant

9/10SubstitutionAM-GMinequalityCasework

Problem

Let x,y,z0x, y, z \ge 0 with at most one of them zero. Find the minimum of

f(x,y,z)=x2+256yzy2+z2+y2+256zxz2+x2+z2+256xyx2+y2.f(x,y,z) = \sqrt{\frac{x^2 + 256yz}{y^2+z^2}} + \sqrt{\frac{y^2 + 256zx}{z^2+x^2}} + \sqrt{\frac{z^2 + 256xy}{x^2+y^2}}.

Answer

Solution

Difficulty9/10
TopicsSubstitution, AM-GM, inequality, Casework

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