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问题: 证明

已知a>0,b>0,c>0且a,b,c,不全相等。求证:(bc/a)+(ac/b)+(ab/c)>a+b+c

解答:

a,b,c∈R+
由基本不等式x^2+y^2≥2xy

(bc/2a)+(ac/2b)≥2√[(bc/2a)(ac/2b)]=2√(abc^2/4ab)=c
(bc/2a)+(ab/2c)≥2√[(bc/2a)(ab/2c)]=2√(acb^2/4ac)=b
(ac/2b)+(ab/2c)≥2√[(ac/2b)(ab/2c)]=2√(bca^2/4bc)=a

三式相加即得:
(bc/a)+(ac/b)+(ab/c)≥a+b+c