c/(a+b)+a/(b+c)+b/(a+c)
>=3{[c/(a+b][a/(b+c)][b/(a+c)]}^(1/3)
=3(abc)^(1/3)/[(a+b)(b+c)(c+a)]^(1/3)
>=3(abc)^(1/3)/[2(ab)^(1/2) *2(bc)^(1/2) *2(ca)^(1/2)]^(1/3)
=3(abc)^(1/3)/[2(abc)^(1/3)]
=3/2