Prove that for all positive x, y, and z,
(x+y)^z+(y+z)^x+(z+x)^y > 2.
(In reply to
Half a solution by Federico Kereki)
Note: Link to posted solution is not working.
Without loss of generality, let x>y>z
(x+y)^z+(y+z)^x+(z+x)^y > (x+y)^x+(y+z)^x+(z+x)^x
> (x+x)^x+(x+x)^x+(x+x)^x = 3*(2x)^x
Prove (2x)^x>2/3
Differentiating and setting = 0 yields x = (e^-1) / 2
and (2x)^x > 0.832 > 2/3
QED
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Posted by Andre
on 2010-05-25 14:09:47 |