xy + yz + xz + x*x + y*y + z*z
6x = 4y = 3z 变换为
x = 2a
y = 3a
z = 4a
原式 = (2*3 + 3*4 + 2*4 + 2*2 + 3*3 + 4*4)*a^2
= (6 + 12 + 8 + 4 + 9 + 16)*a^2
= 55*a^2
= 55/4*x^2
xy + yz + xz + x*x + y*y + z*z
=1/2<(x+y).(x+y)+(y+z).(y+z)+(z+x).(z+x)>
再用那个关系式
^^ ^ what's meaning?