04/11/30 21:41:42
>>681(7) ab/[c(c+a)] + bc/[a(a+b)] + ca/[b(b+c)] ≧ a/(c+a) + b/(b+a) + c/(c+b)
> b/c=x, c/a=y, a/b=z とおくと u=xyz=1.
> 左辺 = x/(y+1) +y/(z+1) +z/(x+1) = [3u +(s^2 -2t) +t +s]/[(x+1)(y+1)(z+1)].
左辺の分子は、xy^2+yz^2+zx^2+(s^2-2t)-s-3 となりますが…