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Tuesday, May 15, 2018

For x,y,z positive numbers such that xyz = 1, prove that: 2 \sqrt{2} (x^7+y^7)(x^7+z^7)(y^7+z^7) \geq \sqrt{(x^{16}+7)(y^{16}+7)(z^{16}+7)}

Solution

2(x^7+y^7)(x^7+z^7) = x^{14} + (x^{14} + 2x^7(y^7+z^7) + 2y^7z^7) by AM-GM: \geq x^{14} + 7x^6y^4z^4 = \frac{x^{16}+7}{x^2} By multiplying similar inequalities and taking square root, we get the desired result

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