That is, s = (x+1) 2+(y+1) 2+(z+1) 2/6 XYZ = (2+x+y+z)/3 XYZ.

x+y+z & gt； 3xyz^ 1/3=√3 XYZ & lt； ((x 2+y 2+z 2)/3) 3/2 =1/3 √ 3 All hold when x=y=z= 1/√3.

So S & gt(2+√3)/√3=3+2√2.