3x-4y-z=0,2x+y-8z=0
11x-33z=0
x=3z
y=2z
x2+y2+z2/xy+yz+2zx这是个齐次式,分子分母都除以z^2
x2+y2+z2/xy+yz+2zx
=(9+4+1)/(6+2+6)
=1.