2x-y-5z=0,
x-2y+2z=0,
3x-12z=0;
x=4z;
y=3z;
x²+y²+z²/xy+yz+zx
=(16z²+9z²+z²)/(12z²+3z²+4z²)
=26/19;
手机提问的朋友在客户端右上角评价点【满意】即可.