if x,y,z are positive real numbers and x+y+z=1 Prove:∑cyc√xy√xy+z≤32
where ∑cyc denotes sums over cyclic permutations of the symbols x,y,z.
Additional info:I'm looking for solutions and hint that using Cauchy-Schwarz and AM-GM because I have background in them.
Things I have done so far: Using AM-GM xy+z≥2 √xy+z≥√2
So manipulating this leads to ∑cyc√xy√xy+z≤∑cyc√xy√2
I stuck here.I'm thinking about applying Cauchy-Schwartz.Also I have not used the assumption x+y+z=1.Any hint is appreciated.
Answer
∑cyc√xy√xy+z≤32
∑cyc√xy√xy+z=∑cyc√xy√xy+1−x−y=∑cyc√xy√(1−x)(1−z)=∑cyc√xy√(y+z)(x+z)
And now, by AM-GM
∑cyc√xy√(y+z)(x+z)≤∑cycx2(x+z)+y2(y+z)=x2(x+z)+y2(y+z)+y2(y+x)+z2(z+x)+z2(z+x)+x2(x+y)=32◻
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