0721132人目の素数さん
2018/09/17(月) 01:23:24.03ID:iDwWzM3i△なのでRavi変換する。
x = b+c-a,
y = c+a-b,
z = a+b-c,
とおくと
x+y+z = a+b+c,
(1)
AM-GM で
a = (y+z)/2 ≧ √(yz),
b = (z+x)/2 ≧ √(zx),
c = (x+y)/2 ≧ √(xy),
より
abc = (y+z)(z+x)(x+y)/8 ≧ xyz,
a,b,c ≧ 0 のとき
abc - (a+b-c)(b+c-a)(c+a-b) = F_1(a,b,c) ≧ 0,
(2)
log(左辺) = a log(a) + b log(b) + c log(c)
≧ y log(a) + z log(b) + x log(c) (←チェビシェフ)
≧ (y/2)log(yz) + (z/2)log(zx) + (x/2)log(xy)
= (y+z)/2 log(z) + (z+x)/2 log(x) + (x+y)/2 log(y)
= a log(z) + b log(x) + c log(y)
= log(右辺),
(3)
(左辺) = (2x)(2y)(2z) + (2x+y+z)(x+2y+z)(x+y+2z) = F1(x,y,z) ≧ 0,