x + y + z = 6 where x,y,z are three positive real numbers. Find the maximum value of (x + y)(y + z)(z + x).
Explanation:
Given, x + y + z = 6.
Let us consider three numbers (x + y), (y + z) and (z + x)
We know, AM ≥ GM
⇒ (x+y)+(y+z)+(z+x)3 ≥ (x + y)(y + z)(z + x)3
⇒ 2(x+y+z)3 ≥ (x + y)(y + z)(z + x)3
⇒ 2×63 ≥ (x + y)(y + z)(z + x)3
⇒ 4 ≥ (x + y)(y + z)(z + x)3
⇒ (x + y)(y + z)(z + x) ≤ 64
Hence, 64.
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