If , , and are positive real numbers such that , then find the minimum value of the following expression
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Relevant wiki: Titu's Lemma
Since a , b , c > 0 we can apply Titu's Lemma
1 + 2 b c a 2 + 1 + 2 a c b 2 + 1 + 2 a b c 2 ≥ 3 + 2 a b + 2 a c + 2 a b ( a + b + c ) 2
Equality holds when a = b = c = 3 1 , substituting we get
1 + 2 b c a 2 + 1 + 2 a c b 2 + 1 + 2 a b c 2 ≥ 3 + 3 ⋅ ( 3 ) 2 2 ( 3 ⋅ 3 1 ) 2 ≥ 5 3 = 0 . 6
Note:
I'm assuming there is a typo in the text of the problem, since if you don't give the constraint that they are positive reals there is no global minimum