olymmath

VN-TST 2006

Vietnam Team Selection Test 2006.

Other problems

Problem 4

Prove that for all real numbers x,y,z∈[1,2]x,y,z \in [1,2] the following inequality always holds: (x+y+z)(1x+1y+1z)≥6(xy+z+yz+x+zx+y).(x+y+z)(\frac{1}{x}+\frac{1}{y}+\frac{1}{z})\geq 6(\frac{x}{y+z}+\frac{y}{z+x}+\frac{z}{x+y}). When does the equality occur?