kuing群里天书问的一个不等式
陈洪葛
posted @ 12 年前
in 不等式
, 1310 阅读
Let a,b,c>0,with a+b+c=3,Prove that
√a3a2+3b2+√b3b2+3c2+√c3c2+3a2≥32
Proof:
∑cyc√a3a2+3b2=6∑cyca2√4a(a+b+c)⋅3(a2+3b2)≥12∑cyca24a(a+b+c)+3(a2+3b2)=12∑cyca27a2+9b2+4ab+4ca
Now,Using the Awesome CYH technology,we have
(∑cyca27a2+9b2+4ab+4ca)[∑cyc(2a+c)2(7a2+9b2+4ab+4ca)]≥[∑cyca(c+2a)]2=(2∑cyca2+∑cycab)2
Thus,it's suffice to check
8(2∑cyca2+∑cycab)2≥∑cyc(2a+c)2(7a2+9b2+4ab+4ca)
Or
∑cyca4+∑cyca2b2+3∑cyca3b−3∑cycab3−2abc∑cyca≥0
Which is not a problem for us now,so we are done!
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