Let ,and the minimum value of the expression is for coprime positive integers , Evaluate .
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Method 1:
By AM-GM, 2 u + v + 2 v + w + 2 w + u ≥ 2 3 3 ( u + v ) ( v + w ) ( w + u ) x 1 + y 1 + z 1 ≥ 3 x y z 3 u + v x + v + w y + w + u z ≥ 3 3 ( u + v ) ( v + w ) ( w + u ) x y z
Multiply the three inequalities together to yield ( u + v + w ) ( x 1 + y 1 + z 1 ) ( u + v x + v + w y + w + u z ) ≥ 2 2 7
m − n = 2 7 − 2 = 2 5
Method 2:
By Holder's Inequality, 2 1 c y c ∑ ( u + v ) ⋅ c y c ∑ x 1 ⋅ c y c ∑ u + v x ≥ 2 3 3
And the result follows.