Let a,b,c be non-negative real numbers such that (a+b)(b+c)(c+a)=0. Find the minimum of (a+b+c)2016(a2016+b20161+b2016+c20161+c2016+a20161).
Solution
When xy+yz+zx=1 and (x+y)(y+z)(z+x)=0, we have x+y1+y+z1+z+x1≥25.(1) Now, WLOG we can assume a2016b2016+b2016c2016+c2016a2016=1. Then, we have a2016+b20161+b2016+c20161+c2016+a20161≥25.(2) Furthermore, by Muirhead and Schur's inequality of degree 3, we have (a+b+c)4032≥(a4032+b4032+c4032+3a1344+b1344+c1344)+i=1∑2015Ci2016(aib2016−i+bic2016−i+cia2016−i)≥24032(a2016b2016+b2016c2016+c2016a2016)=24032. Combining these, we get the minimum value is 5×22015.
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